Bannings Is not the purpose of discourse to expose bad ideas? If we ban people based on what they believe (rather than how they express it according to certain rules of discourse) then that becomes impossible, and discourse has failed. — DingoJones
Holocaust deniers, Neo-Nazis, Racists, Misogynists, etc. don't want to engage in discourse. They want to pontificate. They want to spread ideas to other people, often young people or easily persuadable or naïve people. We are now facing repercussions of major social website such as Facebook or Twitter or YouTube ranging from attempted kidnapping, rallies that end in murder, conspiracy cults, to outright genocide, because they failed to ban such people, and moderate the content on their website.
Others, like Flat-Earthers, 9/11 Truthers etc. are just stupid. No different then someone advocating miasma theory over germ theory.
In both cases, it's perfectly acceptable for the moderators of the website - or whatever platform - to control and maintain the quality of the website. If this site was overrun by racist users and subject matter would you stay? I wouldn't.