Tocqueville, almost 200 years ago, begs to differ:
"I know of no country in which there is so little independence of mind and real freedom of discussion as in America.... in America the majority raises formidable barriers around the liberty of opinion; within these barriers an author may write what he pleases; but woe to him if he goes beyond them." [1]
What's changed this year isn't that Americans are being purged for having the wrong political ideas. That's been happening not for 200 years, but well over 300. Roger Williams, anyone? [2]
What's changed this year is that the major candidate of one of the main two parties holds beliefs that would get any normal American purged. Added to this is the velocity of change: 50 years ago, most normal Americans held these same beliefs. (Heck, not 10 years ago, both Barack Obama and Hillary Clinton were swearing up and down that "marriage is between a man and a woman.")
So you're seeing two processes: an increase in the speed at which America's governing class can evolve its beliefs, and a decrease in their ability to drag the rest of America along with them. No surprise that the latter group wants to respond to an existential threat with an existential threat.
[1] http://dailyprincetonian.com/opinion/2001/10/alexis-de-tocqu... [2] https://en.wikipedia.org/wiki/Roger_Williams