Imagine a post-apocalyptic world in which knowledge of the purpose of cooking had been lost. Many, many fragments of cookbooks remain in existence, but no one knows exactly what they are for -- people in this world eat all of their food raw -- only that their ancestors deemed them very, very important, and that somehow, these rituals are supposed to do something very positive for one and for one's community. (Seriously, it is interesting that someone who doesn't know what cooking is for might be able to read an entire cookbook and still not find out.) Cookbooks become the sacred scriptures of the time, and people perform the recipes in them in very solemn ceremonies, but no one realizes that what is produced was once intended to be eaten and to taste good.
We would find all sorts of conflicting opinions on cooking. Some people would claim that cooking was all just subjective: one merely had to look at the huge variety of recipes put out by different writers of sacred cookbooks to see the truth in that! Others claim that cooking may have once served some evolutionary purpose, but that now it was just a vestige that could be surgically removed without damage to human life. Some people would say that there had been a caste of charlatans called "chefs" who had just made up a bunch of mumbo-jumbo to keep the masses subjugated, too busy in their "kitchens" to rebel. Yet others would claim that it is just a way of promoting communal togetherness, and that, so long as everyone accepts them, the "recipes" can be whatever the community wants them to be, so that we find "recipes" for meat cooked for an hour at 1000 degrees, or for suet, apple, and cyanide pudding.
In this confusion, "authorities" would arise: they would explain to their followers that all true cooking can be rationally derived from some single premise, say, "FIRE = FIRE," or, "The NAP" ("The Non-Aggregation Principle"). The followers of the "FIRE = FIRE" would hold that the single purpose of cooking, indeed of human life, was to thoroughly burn all non-human organic matter. The followers of the NAP would suggest that all peaceful forms of cooking are perfectly fine, just so long as one does not initiate aggregation against non-aggregated ingredients. And, given the confusion all around them, these gurus' theories would have a certain appeal.
The above is an allegory for what Alasdair MacIntyre, in his book After Virtue, claims is the current state of our moral practice: we have lost the telos of morality -- we no longer know what it is for -- and so of course we are in a state of terrible confusion as to how to behave morally. And there simply is no possible way to regain our bearings without recovering that lost telos. If you haven't read it, you ought to.