That's what the field of philosophy is about. I think, for instance, utilitarianism makes a lot more sense than "follow whatever your birth community historically does."
I dunno. Utilitarianism sounds nice on the surface—how can you be against the greatest good for the greatest number?—but it’s pretty under-specified (hedonic or preference? act or rule? do you discount future beings’ utils, and at what rate?) and if you take any particular specification seriously you get moral claims that are wildly counterintuitive, like “insect suffering is orders of magnitude more important than heart disease in humans” or “there may be quadrillions of sentient beings in the far future, and making their lives 1% better is a better use of resources than eradicating malaria now” or “it’s morally justified to steal billions of dollars of other people’s money to give to pandemic prevention and AI safety.” And maybe these are correct claims, but they definitely don’t align with many people’s moral intuitions, and it’d be a tall task to convince those people.
MacIntyre wrote in response to the failures of utilitarianism and deontology, and certain responses to that, so you'd better have arguments for utilitarianism that top those he knew about.
You've also clearly misread him. His argument is that morality is inherently social and good morals necessarily dependent on a good society. To show how deeply connected morals and society are he opts for the use of descriptions of historical societies, because superstition and fantasy alone, like math or thought experiments, just aren't good enough for him. In this he agrees with Marx and disagrees with parts of the analytic tradition in philosophy.
Specifically in After Virtue he also uses such examples to show that the ethics of a society might carry little moral weight, and that some historical societies were better at understanding and teaching morals than his own, in particular the philosophical ethics of the Enlightenment, i.e. deontology and utilitarianism.
If you actually have an argument for why the napkin math morals and disregard of freedom at the center of utilitarianism would be the pinnacle of human ethics I'd really like to hear it.