Because those are what Americans think they believe in, not what they actually believe in when push comes to shove. You overthrow an American-aligned tyrant and you're suddenly a terrorist, the wrong people wield guns and they're suddenly taken away (see: Black Panthers) and I'd certainly like someone to tell the prison-industrial complex about the liberty stuff. Americans like to call these "American values," but if you care at all about these values and take even a cursory look through America's history and at its modern states, the only logical conclusion is to hate America's guts. Therefore, being un-American or anti-American says nothing about one's disposition towards tyranny or liberty.