> Should they be banned too or is communism less directly associated with mass killing and is more in the legitimate ideology territory?
Yes, I think so. It is possible (and, I mean, even basically the default) to be an ideologically consistent communist without any interest in mass killing; that's far more difficult for literal Nazis.
> Historically as practiced communism has involved mass murder of class enemies for political reasons.
I mean, to some extent, what ideology _hasn't_? It's not a core and necessary component of most ideologies, though.