The fact that some beliefs are objectively true, and others not just objectively false but horribly destructive to society, simply never enters your noggin.

A real-world example - a friend of mine eventually kept going on and on about how Muslims were not even human, and should all be killed - as in atom bombing the Middle East.

Should I just smile and say, "That's nice"?

I did not. I tried very hard to argue politely in multiple ways, and at a certain point, probably when I was called a faggot or the like, I cut them off forever.

Many Americans claimed and still claim that the last US election was stolen, even though there is no evidence and many dozens of court cases disproving it, and they mounted an attack on the capitol. Now they're openly announcing that they will never accept an adverse election result again and they will resist using force.

Shrugging and saying, "That's nice!", is not an appropriate response to an all-out attack on your democratic process. (But unfortunately, that seems to be more or less what is happening.)

I happen to live in the Netherlands.

When it came to Fascists occupying this tiny country, many people did not say, "Iemand in zijn waarde laten", "Let's agree to disagree! Why can't we all just get along?" with the Nazis. They fought them, and most of them died, and they are still revered generations later as heroes.

This idea is called the Paradox of Tolerance and it's older than I am.