Every artist that cares about mass market appeal has to self-censor, lest they not offend a large market segment.

That is the point this episode of South Park very deliberately avoids talking about.

Nobody's stopping them from creating art. Really is, unfortunately, putting constraints on which kind of art is going to get bankrolled by millions of dollars of say, Hollywood money.

Those constraints have always been there, and will always be there.

Want free speech? Don't ask for other people's money... They may have opinions about what you should say, using it.