I don't think that saying anti-American is the same as saying un-American. Plenty of people say un-Australian, and I imagine other English-speaking countries s

I don't think that saying anti-American is the same as saying un-American. Plenty of people say un-Australian, and I imagine other English-speaking countries say the same thing (e.g. un-Canadian). It's a way of trying to portray a certain set of values as intrinsic to a particular national identity. In the context of free speech, it makes sense to frame something which some might consider to be a restriction on free speech to be un-American, given that the American constitution explicitly protects free speech. Calling it anti-American would be a different sentiment.