All three things are because of organised religion. Christianity was a driving force behind the longevity of slavery in America. Same with sexism, after all the bible constantly goes on about how women are inferior. It's rather disturbing really.
Regarding not being able to run for president as an atheist, wouldn't black people or women have said the same thing about 30 years ago? Just something I considered.
@Furah, about people being exiled from religious communities for being atheistic, that's an unfortunate side-effect of the reason people believe in the first place; a believer will believe their religion is right and the others are wrong. It's a simple fact, because they wouldn't go for that religion if they didn't believe that.
Its also the main force fighting against letting women have control over their own bodies.