Communism is a political ideology. There were genocidal communists and other who, even if not genocidal, wanted to outlaw Judaism. However there may still be some people who label themselves as communists and have nothing against Jews or Judaism. They might only support the communist economical system, which I dislike, but it's not so evil as nazism.
A nazi is the ultimate evil. There is nothing to discuss with a nazi. If they enter the forum they must be banned. In real life, they must be imprisoned or executed!