It is not unique to the online world, but the online world does change the dynamics around these things significantly, because the social immune system that we have in the real world completely fails on the internet.
In a small, real world friend group "that guy" who talks about ancient aliens, flat earth and Pleiadians or whatever gets shut down real quick and suffers consequences within his social circle.
In the online world, "those guys" can find each other and egg each other on into more bizarre world views. This isn't a theory, you can watch this happen in real time with the qanon "movement".
People who (rightfully) feel estranged by mainstream media or left behind by politics pick up some weird idea, find communities who agree with them and end up holding on to those views longer than they would without the support. In some cases, this leads them to slowly becoming more estranged from real world contacts. Family and friends distance themselves because they don't want to hear any more about how Earth being a globe is somehow a big conspiracy and this little supportive online community eventually remains the only safe space to talk openly and they become more invested in it.
The problem is these communities harshly punish everyone who disagrees with the mob. Increasingly outlandish ideas are pushed into the conversation, and your only options are to agree or to be turned away, which becomes increasingly painful the more other contacts withdraw from you. It's a death spiral that is scary effective.
Eventually the only people that you can relate with is a group that also talks about how every bad thing that happens is orchestrated, democrats are all traitors that need to be put in front of a firing squad and baking soda treats cancer.
We need to come up with something to fight this deterioration of the social fabric, but I agree censorship is not sufficient or maybe even helpful.