> If society can not out-argue "The Nazis" in open debate, then what is going on?

What's going on is that the world isn't a debate club and the Nazis aren't interested in playing by the rules of the fair fight you want to give them:

“Never believe that anti-Semites are completely unaware of the absurdity
of their replies. They know that their remarks are frivolous, open to
challenge. But they are amusing themselves, for it is their adversary
who is obliged to use words responsibly, since he believes in words.

The anti-Semites have the right to play. They even like to play with
discourse for, by giving ridiculous reasons, they discredit the seriousness
of their interlocutors. They delight in acting in bad faith, since they
seek not to persuade by sound argument but to intimidate and disconcert.

If you press them too closely, they will abruptly fall silent, loftily
indicating by some phrase that the time for argument is past.”

― Jean-Paul Sartre

By trying to engage dishonest people in honest debate, you're only making a fool of yourself. Why? Because the playing field isn't level. Radicalization is much easier than deprogramming, and lies spread much more quickly than truth, because most human beings aren't swayed by logic and reason, but by emotion, ego and self-interest. There aren't enough of the rest to matter.

Take QAnon for example. That went from a meme on 4chan to a political cult powerful enough to affect national politics and fuel an attempted insurrection. Do you think no one has ever tried to explain the error of these people's ways to them? Did the years of having them "exposed to sunlight" on all social media platforms do anything but increase their spread and their toxicity?

Anti-vaxxers have been freely spreading their beliefs online for years. Has any of the debate or criticism actually stopped the movement, or even slowed it down?

Can you even name one example where a violent political movement or conspiracy theory was stopped through nothing but polite debate?

>If an idea is bad, the worst one can do is just try to censor it completely, that if anything let's people know that one is afraid of their ideas.

The implication is that people will believe one is afraid of their ideas because they might be true. There may be some people who think that way, but most people don't. And honestly, I was fine with these people being quarantined on Parler and Gab, and if they had been able to simply discuss their views without using their platform to put them into practice they would still be there. But speech doesn't exist in a vacuum, it exists in a context and Nazis intend to put their ideas into practice. Trump supporters and QAnons planned to "stop the steal" by kidnapping and killing elected officials. Anti-vaxxers plan to undermine America's vaccination attempts and destroy herd immunity.

So yes, I'd rather try to at least slow down their ability to recruit and radicalize people by not giving them carte blanche on the biggest social and political power multiplying platforms humanity has ever created. If that means some fools suddenly think anti-semitism and crystal healing are hip because they're forbidden, let them stay on /pol/ and make stupid memes.

>Such things come back to bit oneself. (Using the term "one" here rather than "you" to avoid sounding accusatory)

Such things bite even harder when left alone to gather strength in numbers.

>Allowing others to discern the quality of speech is ofcourse part of the whole deal. The border being crossed here goes somewhere along the lines of the current cancel-culture trajectory.

The people with a vested interest in spreading hatred and fear of "the left" have gone so far off the deep end with hyperbole and scare-mongering about "cancel culture" that they've rendered the term as meaningless as "socialist" and "SJW."

But, of all the arguments you could make against cancel culture, it getting used against Nazis, violent seditionists and cranks isn't the most convincing.