A lot of those kinds of atheists had been religious at one stage and had a reaction considerably the same as an event that causes people to be racist.

Anyway, they end up hating religion because of what religion did to them.

Personally I'm deist, I believing in God but I was never naive enough to be brainwashed into some pathetic religion and used and controlled like some atheists were, so I never grew up to resent the belief in God, yet I still remain rational in my beliefs.