How many of you guys in the US even know about restroom access cards?

[FenKit]

Then how is it possible that communism was illegal in the US? I don't understand.

Unless you are directly acting against the United States, which would be treason, you cannot be prosecuted for holding a certain political belief.

Unfortunately, the “red scare” gripped people so much that to an extent they threw out freedom of speech out of fear that communism would take over. It wasn’t inherently illegal, but you were more likely to be charged with treason just for agreeing with the ideology.