Ghengis Khan exterminated everyone in huge swaths of the regions he conquered (even says so in Civ4), Stalin exterminated millions of his own people via forced collectivization and forced labor camps, and of course there was the human sacrifice the Aztecs practiced: yet these civs are in the games we play. Is it because you don't actually need to make these atrocities part of your gaming strategy (like you would in Col) when you play these civs?
Yes, I haven't played it for years, but I don't remember Col providing cultural or diplomatic victory conditions. I assume these would be included in any remake, as they're standard in Civ now. Would really improve the game, too.
Maybe it's just the 'narrower focus' that has caused Col to be ignored. Slavery was virtually ignored in Col (and other strategy games) but is shamelessly in Civ 4.
As you point out, it seems that most if not ALL civilizations are capable of horrendous acts, I guess we feel more guilty about our own Civ
