As we talked about altruistic behavior towards other species, there is no gain for the altruistic "gene" by improving fecundity or viability of an other carrier of that gene for example.
Altruism and selfishness are not genetic or hard-wired as much as they are learned, social behaviors. But regardless, talking about evolutionary alignment is pretty insane, IMO. Gold Dragons are "good" to show that not every dragon is there just to be killed, and to provide a different kind of challenge for a party, and to make a world in which there is one a richer place, and to provide homage to all the good, pure, sacred dragons in myth and legend, to give the party a powerful dragon patron, to represent the fantasy trope of "it looks on the outside like it is on the inside (beautiful and good, ugly and evil)," etc., etc., etc.
A D&D game that doesn't want to represent basic fantasy storytelling techniques isn't a good game for my group, because that is important for my group. Being able to kill a Gold dragon without changing the alignment is NOT important for my group, really, in the slightest. I've lost something constructive, nothing constructive was added, this was an idiot choice from my perspective.
And I really wonder why the 4e team even kept alignment in the game if it's just going to be "PC's Good, everyone else Not Good." If all you use the Good alignment for is to give PC's the right to stab things, it's not being used in a heroic or noble narrative context at all. May as well take the thing out of the game, especially given the mercenary nature of most PC parties.