Is believing in Anarchism illegal in the USA? I don’t think so. The only way in the USA to get on a watchlist is to be either a high felony criminal or a terrorist. Neither the CIA nor the FBI have the time and resources to monitor everyone at the same time.

It’ll probably slap you on a watchlist, but that’s not really a huge accomplishment. As far as getting charged, it depends on where you live and what you say. If you start talking about blowing up buildings or something, well, I hope you have a good lawyer on retainer before the feds hunt you down.