This is a sticky issue, with two contradictory principles.
On one hand, sites - just like any physical locale - should have the necessary freedoms to determine what kind of user experience it offers visitors. If you go off on a conspiracy theory tirade in a quiet restaurant, you will probably be asked to leave because your behaviour prevents other clients from having the experience they want and expect from the restaurant. This does not by any reasonable standard constitute a violation of your freedom of speech. If it works for physical locales, then surely it must also apply to websites - because just like restaurants, websites offer certain experiences in order to attract certain kinds of visitors.
On the other hand, a guaranteed right to do something is meaningless without a similarly guaranteed right to the means necessary to do that thing. A great deal of discourse and organisation - political of otherwise - these days happen on the internet, so if it is held that people can be excluded from online discussions does that not also mean that it is held that people do not have the guaranteed right to fully participate in civil society?
I’m inclined to say that any blanket treatment of the issue will be a bad idea.