I'm a bit wary of this.
"Bolshevik" comes from the Russian word for "Majority" and might be used in a Russian-language nation to refer to a majority sect in general (I defer in advance to any Russian speakers present on this). I also second the points on "Soviet" being a "Worker's Council" of sorts. I'm not going to debate the ban on Nazis because it was always a contentious issue to permit it; for all I know there might have been a wave of intolerant idiots in the past two years.
I admit that it would be better for RP if players invented new terms for these, but there's a risk of this being viewed as banning the concept rather than the terms. The reason behind past permissiveness was for diversity in RP: as much as using the exact same terms is a little unimaginative, if the extreme concepts are banned and we end up with a world of SocDem, Lib, NeoCon and Green parties, it'll be a backward step. Besides, it's fun to play the bad guy in RP every now and again...
Nazi systems --of the word itself-- were in one country, whereas many more became Soviet Socialist Republics or had parties that advocated becoming one. I would argue that the latter's breadth should permit at least the inclusion of "Soviet".