Those who respond to periods of rapid and disruptive change by appealing for a retention of or a return to the ways of the past, to the customary, to the traditional, always have to reckon with the fact that in an established customary social order those who follow its ways do not have and do not need good reasons for so doing .... It is only later when these routines [of the normal day, month, and year] have more largely and more radically been disrupted that the question of whether it was not in fact better to follow the older ways unreflectively can be raised, and when the conservative offers his contemporaries good reasons for returning to an earlier relatively unreflective mode of social life, his very modes of advocacy provide evidence that what he recommends is no longer possible. So in Aristophanes' comedies the conservative figures portrayed are in part comic victims because forced into the very rhetorical modes which they abhor in order to argue against those modes.
This is a difficult yet intriguing passage. As a first pass, I think I can understand it by considering the arguments for `traditional family values' and against redistributive welfare, affirmative action programmes, and the progressive cultural transformations of the mid- and late-twentieth century more generally.
Note first that these conservatives generally do not argue that these programmes and transformations are bad because they harm members of privileged classes by taking away some of their privileges. For example, no opponents of affirmative action programmes argue that making it harder for wealthy white people to get into prestigious universities is, in and of itself, a bad thing. Similarly, no advocate of `traditional family values' argues that women need to be full-time homemakers so that men can enjoy less competition in the workplace.
Note second that the arguments we actually see are, instead, that these programmes and transformations harm members of the classes they are intended to help. Affirmative action is tantamount to grade inflation, and will just end promoting people beyond their real ability, being on welfare is demeaning, women who work outside the home are too busy to be good mothers, and so on.
In short, racists and sexists no longer feel they can appeal to racist and sexist principles to criticise anti-racist and anti-sexist policies, at least explicitly. Instead, they attempt to appropriate and turn anti-racist and anti-sexist principles. Affirmative action and welfare programmes are racist, it's sexist to encourage women to work outside the home, and so on. Just as MacIntyre says, the sexist and racist routines of sixty years ago have been largely replaced with more progressive routines, and even conservative opponents of our contemporary routines must argue their case in the conceptual framework of these same routines.
This does not entail that conservatives can never be successful, at least in the middle term. Anyone who is familiar with the history of the anti-feminist backlashes in the wake of the First and Second Waves will know just how successful conservatives can be. But even when conservatives are successful, their success is not a true return to the old routines. What conservatives can accomplish is a synthesis of the conservative thesis and progressive antithesis: a social order which rejects some, but not all, aspects of the progressive order as `excessive'.