Why do Athiests study religion just to tell someone they're wrong?

Many Atheists I know like to study mostly Christianity just to throw it into the face of a Christian. If you feel you are so intelligent then why not use those skills for something useful instead of trying to destroy someones faith? I know I'm gonna get alot of flak from you people saying that God is fake!, Snakes don't talk, we started all the wars, etc. but, I wouldn't mind a serious answer.