>No, there is certain content that is forbidden by law in some countries, for example Holocaust denial, Nazi propaganda and other racist or otherwise discriminatory content. I do wonder why Youtube and Twitter don't disallow that kind of stuff by default, there's no reason for giving this kind of content any platform even if it's legal by law in the US.

I think you are confusing things. Simply because you desire forbidding others the choice of whether or not to view the content does not in any way mean that the act of suspending a channel doesn't accomplish this. The reason it is a horrendously dangerous, terrible, horrible idea to acede to a desire to hide 'dangerous' information would, I would hope, be easily seen by now, but it's obvious that this isn't the case. People seem to have forgotten that the Nazi newspaper was banned by the government of Germany after the Beer Hall Putsch. They seem to have forgotten that prior to that, the Nazi party was some guys hanging out in a pub being angry, and once the disliked establishment banned their paper it became the thing every German 'had to read'. They seem to have forgotten that it was the exact kind of censorship they seek to enact today that catapulted Hitler and his party into the forebrain of every downtrodden German.

The only legitimate and adequate response to a bad idea is a better idea. Full stop. You can not ban an idea. You can, however, drive it into hiding where it will see no opposition, no correction, no competing evidence. At that point, you guarantee for yourself the creation of an insular subculture who will draw the disaffected and opposition to the establishment. It is a Bad Idea. It has always been a Bad Idea. There has never been a happy state with heavy censorship.

Had we had such censorship in the 1960s, interracial marriage would still be illegal. Had we had it in the 1800s, slavery would still be legal. Every progress of mankind begins with spitting in the face of the established order. And that Nazi morons are clearly not a part of such progress is of no great import. You (generally, in the 'your society' sense of you) will be incapable of judging the next step of progress and this is guaranteed. In the United States, there is a legal concept called Prior Restraint on free speech and it is very aggressively avoided by the courts, as well it should be.

You are incorrect that various fringe groups would be smaller if YouTube became a bastion of censorship, and also that the platform owner is responsible for problems that you believe resulted from ideas being available. The existence of the fringe groups, their sizes, and the problems are all a result of widespread anti-intellectualism and a rejection of critical thinking and reason as an acceptable means of determining ones beliefs. Things like the anti-vaccine movement in particular grow far more through word-of-mouth than they do online resources. Zero of the anti-vaxxers went online to seek information about vaccines and found anti-vaccine ranting and then made a decision to not vaccinate their children. Instead, they heard about it from mothers who "just knew" that vaccines gave their kids autism. Or they listened to their president talking about how there are "just too many" with no basis. The idea that vaccines are harmful, that letting strangers, intellectual strangers who don't care, stick steel needles into their children and inject them full of chemicals and dead viruses was dangerous felt right and that is literally the only thing in the world that could convince them of any position.