Is your basic thesis here that (a) because "morals" are, for the most part, based on something that is not rational, and (b) because most people will nonetheless do their best to justify even the most irrational of their morals, (c) there is therefore no point in trying to construct a morality that is based in rationality?

That's what it sounds like, but I wanted to make sure I had it right before launching into commentary...