Christians did support eugenics laws even when the Supreme Court struck them down in the 1970s.
That's quite a sweeping generalization. I'd say "ignorant people including religious fundamentalists" because there are other religions who support that sort of thing as well as quite a few atheists and agnostics.
"Christians" don't have a monopoly on idiocy. Besides, I've known plenty of Muslims, Hindi, Buddhists, Christians who have less hate and spite and are more genuinely altruistic than those who are blindly hateful towards people with some (or some other) faith system.
People find a way to use religious systems as an easy way to justify hate and intolerance, but there are many people who use their intellect to justify hate and intolerance if it serves their personal needs (greed and avarice as examples.)