I intended to write a comment with an explanation of how genocide can't be committed against a group formed by a shared ideology. I was going to illustrate my explanation by pointing to the extermination of Nazism. However, according to the definition on Wikipedia, genocide includes the destruction of, or the attempt to destroy, a national or religious group. The Sith certainly fit within that definition. So it turns out that the Allies committed genocide when they wiped out Nazism.
According to the definition, genocide is not mass murder. It is merely destruction.
Your comment seems to imply that you think that I disapprove of the destruction of Nazism. Let me be clear: I think Nazism is evil and I'm glad it was destroyed. My comment was only pointing out that the destruction of Nazism was genocide by definition.
http://en.wikipedia.org/wiki/Genocide