Dostoyevsky wrote that "if God does not exist everything is permitted" . MacIntyre maintains that this is mistaken and in fact turns it around, as we shall see. He tells us,
Theism furnishes an explanation for the authority and the fixed character of the rules, both by according to them divine status and by providing grounds for the underlying belief in a single determinate human nature. God created men with just those goals, wants, and needs which a way of life embodying the given rules will enable them to achieve. To the natural morality of men theism adds rules concerned with man's supernatural end, and a set of beliefs and practices concerning guilt, repentance, and forgiveness to provide for moral, as well as religious, failure. Theism and morality of this kind naturally and easily reinforce one another. I think, moreover, that theologians have this kind of morality in mind when they assert that the loss of theistic belief will bring about, or has brought about, a loss of morality. In this last we recognize Dostoyevsky's assertion, plainly stated. MacIntyre continues,
My central thesis is the direct opposite of their view: I hold not that a loss of theistic belief produces a loss of moral belief and a change of practice, but rather that a change in the character of morality is at least partly responsible for the modern inability to accept theistic belief. That is, I wish to invert the Dostoyevskian contention about the relation between theism and morals. [38-39]Theism requires, MacIntyre maintains, a a particular position with respect to morality: more specifically, if theism
is to be coherent [it] must rely . . . upon an independently understood moral vocabulary. To this conclusion I now wish to add another and stronger thesis: namely that theistic practice depends upon the existence of independent moral practices. Moral practices, he makes plain, which have ceased to be common today. But what exactly is he getting at? He asks us to consider why someone obeys the law against stealing. There are essentially two reasons. First, because if you don't you may get caught and punished. The second reason you might not steal is because you find it beneficial to live in a society in which you can generally depend on the things you own being there when you need them. Laws which rely on both of these command our respect as well as our acquiescence. On the other hand,
A legal code which arbitrarily ordains and prohibits actions that are without reasonable point or purpose commands our allegiance only insofar as it is able to deploy power to enforce its sanctions. As with legal code in general, so also with divine law. if God's commands are not to be mere fiats backed by arbitrary power then they must command actions which can be seen to have point and purpose independent of, and antecedent to, the divine utterance of divine law. [35-36]Many theists today miss the importance of this point when they argue that what is good is good because God declares it to be good. This is clearly erroneous, according to MacIntyre.
What I wish to show is that this view is internally incoherent, and the most vivid way in which I can begin to show this is by pointing out that it is difficult, if this view is correct, for theists to distinguish between God and the devil in the way that they must. For if "God is good" and "We ought to do whatever God commands" are transformed into tautologies by means of redefinitions of "good" and "right," it follows that we can have no moral reasons for obedience to divine commandments. In this scenario God's benevolence is unjudgable. God must therefore be regarded as "right" simply because we know his omnipotence rather than because we know his omnibenevolence. Furthermore the devil is "wrong" not because of his anti-benevolence but simply due to his lack of omnipotence. "God," MacIntyre remarks,
has been transformed by the proponents of this view into a Hobbesian sovereign whose title to legitimate authority rests not on his absolute paternal care, his goodness as a father, but solely on his power, and the devil's lack of such a title rests solely on his inferiority in respect of power. Satan becomes a Hobbesian rebel who fails to be a Hobbesian sovereign only because he is unsuccessful. Christian theism in particular can scarcely tolerate this. . . . Now we begin to understand clearly why MacIntyre considers it so important to maintain that morality is something independent of God. But just as morality must be something independent of God's decisions and judgments, so it must also be something independent of our human decisions and judgments.
What morality is required to be by theism and what it usually has been considered to be is a set of rules which are taken as given and are seen as having validity and authority independent of any external values or judgments. It is essential to morality so conceived that we accept the rules wholly and without question. We must not seek rational grounds for accepting them, nor can we decide, on rational grounds, to revise them—although we may discover by chance that we were mistaken in what we thought the content of the rules to be. When morality is considered in this light, theories about morality are accounts of why the code of moral rules includes the items that it does and no others. Platonic and Aristotelian morality both offer theories of this kind. Aristotelianism grounds its explanation in the view that human nature has certain inherent goals, needs, and wants. The cogency of this theoretical explanation depends on the fact that the society which upholds the given moral rules agrees upon a way of life defined in terms of just those goals, wants, and needs. [37-38]But that last point is just the problem today, MacIntyre asserts. Western society no longer agrees on goals, wants, or needs—nor even accedes that there can even in principle be agreement on goals, wants, or needs. Instead two inimical beliefs have risen to the forefront of modern thought.
The first of these beliefs is that disagreements between rival moral views are essentially irreconcilable, that there is no shared criteria to which men may appeal in order to settle fundamental disputes. . . . The obvious counterpart to the idea that fundamental moral disputes are in principle irreconcilable is the belief that there is not just a single determinate human nature; that human nature is immensely malleable; and that around the relatively unchanging biological core society and culture may weave very different patterns, resulting in widely varying wants, needs, and goals. It is just because this belief is dominant now that no ultimate shared criteria can be invoked by which moral disputes may be resolved. That is the predicament we face today. It is the predicament faced by theism, but it is also the predicament faced by the secularist, agnostic and atheist. In fact MacIntyre warns atheists against expressing too much glee at the difficulties faced by theists because of this sea-change in the modern moral framework. After all, this development has "placed not only theism but also its atheistic critics in a position where their debates cannot supply contemporary cultural needs." 
In fact, to a significant extent it is the failure of atheism and secularism to develop a non-religious moral framework capable of reconciling the current moral anarchy and restoring belief in a "determinant human nature" which has allowed us to end up where we are. For if it is true, as MacIntyre has convincingly argued, that morality is properly independent of theism, then it is absolutely necessary for atheists and secularists to provide a non-religious vocabulary "for the traditional religious and moral questions."  Atheists have not been up to the task, to say the least.
Before ending, we might ask how and why the "traditional attitude to moral rules" became overturned. Although there are many causes, MacIntyre sees two as most influential. The first
was the impact of those versions of Christianity—mainly Protestant, but in some cases Catholic—according to which human nature is seen as so corrupt that human morality must be considered of no account. The consequence of this view is that from any human standpoint the divine commandments do become arbitrary fiats imposed on us externally; our nature does not summon us to obey them, because we cannot recognize them as being for our good. The motives of hope of eternal reward and fear of eternal punishment then must completely replace temporal motives for morality. The second (and perhaps more important) influential cause requires more exposition and therefore warrants a longer quote from MacIntyre's lecture.
A second tendency also inimical to that morality was that embodied in the liberal principle that the individual is sovereign within the sphere of morality. In classical liberalism this principle is often and significantly expressed in an incoherent form. For it is first of all presented as itself an objective truth whose moral validity and authority in no way depend upon individual moral agents' assenting to it or deciding to make it their own; and yet since the right that it ostensibly confers upon the individual is an unrestricted right to make his own decisions as to what principles shall be binding upon him, it is a self-destructive principle. Certainly the picture derived from it of each individual as uttering moral injunctions to himself which gain their authority from no source other than his own will and choice is inconsistent with the morality that theism requires. Kant's moral philosophy will provide us with illumination at this point, for Kant wrote at a key period for the history of the relations between theism and morality, when the rift between them had become clearly apparent, and morality had half, but only half, changed its character. It is an undergraduate-essay commonplace that Kantian ethics is riddled with incoherences. The possibility that is treated with inadequate seriousness is that Kant was not in fact for the most part the incoherent and inconsistent analyst of a set of coherent and consistent moral concepts, implied in the practice and utterance of ordinary moral agents, but rather that Kant was the coherent and consistent recorder and analyst of an incoherent and inconsistent set of moral concepts which were embodied in an incoherent and inconsistent moral practice, and one that had become so as a consequence of the very tendencies which I have been noting. Kant, if we read him thus, provides us with confirmatory evidence on a number of matters. The autonomy of morality he recognizes when he asserts that men cannot derive it from theism if they are to call God or "the Holy One of Israel" good in any significant sense; yet he still invokes a theistic explanation to give morality point. He must do so, since for Kant the heterogeneity, the variety, the incompatibility, which mark man's natural goals, needs, and wants entail that these can provide us with no stable criteria. He cannot find, as the medieval Aristotelian would, any point or proof for morality in terms of the satisfaction of the needs and wants of a human nature created by God to be of a certain determinate kind; and he invokes theism only as an assurance that goodness will be rewarded in another life. While theism is assigned this attenuated role, the autonomous moral agent is presented as one whose moral prescriptions have no authority other than that derived from himself as a rational agent and yet have the character of a law.MacIntyre misses one of the essential aspects of the milieu in which the victory of liberal individualism developed. Platonic and Aristotelian morality depends not just on a universal acceptance of a fixed human moral nature, but also on a society with the type of power-system in which that universal acceptance can be forced on the population at large. Autocratic societies pretend otherwise, but ultimately humans exist as individuals and human actions occur as individual actions. All moral behavior—as is all behavior—is necessarily carried out by individuals.
But what authority can a law have which I utter to myself? And what sanction can a law have of which I am expressly told that there are no earthly sanctions to back it and when the theistic sanction is invoked to make morality theoretically intelligible rather than to provide one with a motive? In other words, in Kant's writings the notion of morality as a law, and with it the traditional notion of one true morality, is combined with a liberal individualist recognition of the individual's sovereignty, and so is considered as a law only in some rather curious sense at best; and this unstable combination was indeed bound to lead to a victory for the liberal individualist elements of the conceptual scheme and a defeat for those elements derived from the traditional ways of regarding morality. And this is because these matters were not merely episodes in the intellectual history of theology and philosophy, but stood in intimate relationship to what was happening in society at large. For the morality that had become so irrelevant in theory was having its roots in social practice destroyed by a rate and type of social change which made ordinary men far more conscious of actual and potential variety of competing and conflicting moralities and ways of life and the need to choose between them, and thus it was undermining the notion of one true morality. [40-43]
What changed with the enlightenment is that individuals began to claim the right to govern themselves and began throwing off the autocratic governing previously done by Kings, Aristocrats and Popes. Instead of being controlled top-down, Western societies began to be controlled bottom-up. This meant in practice that moral decisions, like political ones, began to be made in a manner more representative of individuals themselves.
The shift in the moral framework which fuels MacIntyre's pessimism occurred precisely with the shift to democracy and the concurrent desire that morality like politics also be controller bottom-up rather than top-down. MacIntyre is pessimistic precisely because he recognizes that this shift is not reversable while at the same time he perceives its harmful effect on theism.
Here MacIntyre and I part company, because my perception is that the democratization of morality will in the long run be positive specifically because I believe there is a more-or-less determinate human moral nature, one written not by God but by our evolutionary past. Whereas MacIntyre sees the individualization of morality in terms of a pandora's box, I see it in terms of a democratization which moves power (in this case moral power) to its biologically correct position, that is to say, to the individual.
Nevertheless, MacIntyre is entirely right when he points out that the current result is that morality has lost its "moral force", and that this loss is due to the fact that Western societies (and particularly American society) no longer believe in a determinate human nature and believe consequencely that moral disagreements are, in MacIntyre' phrase, "essentially irreconcilable". The core ideology of multiculturalism, for example, is that no culture can legitimately judge the practices of any other culture as inferior or superior, or as right or wrong—for there is no valid external reference point to act as a fulcrum for such a judgment.
I am out of time and have to stop here, at least for the moment.
MacIntyre has laid down the challenge. Can we provide an adequate and convincing atheistic moral framework to replace what has been lost?