They aren't banned in any sense whatsoever - there's a communist party in USA, they're free to publish their views, do rallies, advocate their position, run for elections, and they're "banned" only in the sense that almost noone votes for them or supports their views.
That's the exact treatment that Nazis, ISIS, North American Man/Boy Love Association and all kinds of other disgusting groups should get - they should be free to associate and state their views publicly, so that the public can hear them, be disgusted, and vote against them. If some of them do violent acts or incite violence, then those particular people can and should be charged appropriately, but not the rest of the group.
You are technically incorrect (the worst kind of incorrect).
See, for example, the [Communist Control Act of 1954][0], various [state laws][1] [that prohibit communists from holding office or working in state jobs][2], and [exclusion from anti-discrimination laws][3]
Do you mean the act that, according to the same source, "no administration has tried to enforce" and whenever states have attempted to do similar things, the restriction has been found unconstitutional (e.g. Blawis v. Bolin)?
The USA legislation has a bunch of things "on the books" in their legislation that haven't been repealed since noone wants to touch them (e.g. sodomy laws), but aren't law in any practical sense since they aren't and cannot be enforced.
Despite the things you quote, the Communist party of USA does exist, can participate in elections and has done so. Of course, almost noone votes for them, but that's their own fault.
Many of the proposals and discussions in this thread are very similar to McCarthyism. Just as it was back then, despite people wanting to do so, the key acts and limitations of McCarthyism are fundamentally incompatible with Constitution of USA; just as it was (found to be) wrong and overstepping authority regarding communism back then (even if it took a bunch of years for the courts to override all the activism of the government), it's the same thing for any other radical ideologies now.
That's the exact treatment that Nazis, ISIS, North American Man/Boy Love Association and all kinds of other disgusting groups should get - they should be free to associate and state their views publicly, so that the public can hear them, be disgusted, and vote against them. If some of them do violent acts or incite violence, then those particular people can and should be charged appropriately, but not the rest of the group.