Actually, just the opposite of what you are saying here is true.   It was Christian Churches that have led the way in fighting things like slavery and discrimination against homosexuals.   The entire Abolitionist Movement movement before the Civil War was first created and supported in churches.

And not one single US church ever endorsed or supported the KKK in any way.   You are re-writing American history to fit your own personal make-believe fantasy.   The KKK itself was extremely bigoted against both Catholics and Jews.

Atheists like Adolph Hitler, Joseph Stalin, and Mao Zedong have exterminated millions.    And it was Muslims who were responsible for the horrific Armenian Genocide that took place during WWI.   

The monstrous number of innocent civilians that have been killed in Afghanistan and Iraq in recent decades has been primarily due to Muslim vs Muslim violence.    The number of civilians that have been killed by America's military in those nations is very, very low.