Actually Tom, the most vocal of the "radical left" that I've heard have been Christians themselves. They simply seem to go against the neocon Christian fundamentalists. As for myself and a good number of other atheists I've known, the politics usually falls more into the centrist viewpoints.

I do challenge your statement that atheists have been guilty of many atrocities throughout history. Compared to the damage done to humanity by people of faith, the atheists hardly show up on the radar screen. It's much simpler to send a fellow human being to their maker if you actually believe in one.