If I had a penny for every time a theist told me that on many occasions in history, atheism has been the cause of genocide...particularly Pol Pot, Hitler and Stalin.
I wrote a blog post about Hitler and Stalin in particular over at my blog: http://www.odd-innuendo.net. I won't bother reposting it here, as I would just be preaching to the choir.
I'm getting tired and frustrated. Maybe I need to take a break and do what I enjoy...photography and art...but then again, I just can't keep away from debate!