Here's a hypothetical, not too far removed from reality: What if I discovered, to my satisfaction, that moral reflection -- the kind of intellectual thinking about ethical issues that is near the center of moral philosophy -- tended to lead people toward less true (or, if you prefer, more noxious) moral views than they started with? And what if, because of that, it tended also to lead people toward somewhat worse moral behavior overall? And suppose I saw no reason to think myself likely to be an exception to that tendency. Should I abandon moral reflection?
What is the point of moral reflection?
If the point is to discover what is really morally the case -- well, there's reason to doubt that philosophical styles of moral reflection are highly effective at achieving that goal. Philosophers' moral theories are often simplistic, problematic, totalizing -- too rigid in some places, too flexible in others, recruitable for clever justifications of noxious behavior, from sexual harassment to Nazism to sadistic parenting choices. Uncle Irv, who never read Kant or Mill and has little patience for the sorts of intellectual exercises we philosophers love, might have much better moral knowledge than most philosophers; and you and I might have had better moral knowledge than we do, had we shared his skepticism about philosophy.
If the point of philosophical moral reflection is to transform oneself into a morally better person -- well, there are reasons to doubt it has that effect, too.
But I would not give it up. I would not give it up, even at some moderate cost to my moral knowledge and moral behavior. Uncle Irv is missing something. And a world of Uncle Irvs would be a world vastly worse than this world, in a way I care about -- much as, perhaps, a world without metaphysical speculation would be worse than this world, even if metaphysical speculation is mostly bunk, or a world without bad art would be worse than this world or a world of a hundred billion contented cows would be worse than this world.
If I think about what I want in a world, I want people struggling to think through morality, even if they mostly fail -- even if that struggle rather more often brings them down than up.