Consider to what extent you're steeped in the mire accumulated from being very-online. If you agreed with everything else, then that should give you pause on why you're so hesitant or resistant to that usage.
If I didn't use the Internet I wouldn't know what the term 'anti-American" meant. Nobody I know uses that word and no books I read or movies I watch mention it too. It is a term that I've encountered only on the internet. As a result, my connotation of the word depends largely on how the internet uses it.
On the websites I visit, the term "anti-American" is usually used to justify hate against minorities or some other segment of society. I'm sure it is used in different contexts too (in other parts of the internet), but not on the parts of internet I usually browse.
The red scare didn't need Facebook to get started.
Claiming something is un-American is fine. We're (mostly?) red-blooded Americans here.
However, pointing at something and saying it's un-American and expecting the crowd to gasp in horror and join you in denouncing it, is a very clear signal of a Fox-news-or-something-deadened brain.