Non-American here.
I lived in the United States for over thirty years. My experience was different.
I lost a lot of friends in the last ten years, because they started posting completely ridiculous, crazy stuff and were completely defensive of even the most reasonable objections.
I'd put up with "Obama is a Muslim" for a long time, but then it started to escalate. People would get hostile when you mentioned that there were records showing otherwise. After the election, some people become convinced that Michelle Obama was in fact a transgender man and let me hear all about it.
And you know, it's hard not to get a little pissed off about such blatant lies, hmm?
A long-time friend of mine started posting about Sandy Hook being a hoax - that the school had never existed. I pointed out that a friend-of-a-friend of mine had lost two children there, and my friend just went ballistic and started calling me the most unbelievable names, "Do your homework!" I unfriended her. You could see her get more unhinged on other people's pages and unfriended, and I haven't heard anything from her in years.
And now we have terrible lies about medical data, and again, people become incredibly defensive. At least two acquaintances accused me of being a pharmaceutical company shill! (I've never worked anything remotely like that.)
Sorry, it's not just "politeness" - a significant portion of Americans just went off the rails in the last decade.