Using selfish game theories, "generous" or "altruistic" strategies can evolve to dominate in iterated games and evolved populations (there's a link somewhere upthread to the paper). You're still then left with the question of: if they do, why did evolution build us to place fundamental emotional and normative value on conforming to what any rational selfish agent will figure out?

Because we're adaptation executors, not fitness maximizers. Evolution gets us to do useful things by having us derive emotional value directly from doing those things, not by introducing the extra indirect step of moulding us into rational calculators who first have to consciously compute what's most useful.