I think people who are too similar find ways to hate each other. Catholics v. Protestants in Ireland (and elsewhere), Greeks v. Turks, Middle Eastern Christians, Jews and Muslims, whatever.

If you got rid of every non-Christian in America, they'd divvy up by Protestants, Catholics, Mormons, et. al. If the Protestants won, they'd divvy up by sect. And, to quote Dennis Miller from back when he was funny, it would get down to one guy and he'd attack his image in the mirror.