Two of the moderation issues that I can think of are 1.) volume of information, and 2.) depth of knowledge.
Some unpopular views are overly represented on any platform. This is the reason why far left/right get amplified to be more mainstream opinions, despite being truly unpopular. Another thing is similar to self-censorship like you mentioned, but self-censorship in the sense that if you feel that the community has shifted towards a certain bent, then one might move on from that community, since it no longer represents what they're looking for/what they feel is right.
Finding legitimate information is also tough: there's been instances of journal-published data that was verifiably false, since the journal that it was published in was founded in order to push specific data/viewpoints. But, the average person doesn't know that, and probably won't be familiar with what journals are popular, legitimate, etc. While some people (you, I, and probably others on this platform) like delving deep into this sort of stuff, most people (I'm venturing a guess here) would stop short at "research shows that..." when fact-checking something.
I wouldn't argue _for_ banning, or at least would argue that there's a better way to do it that doesn't also burn people who are participating in good faith. But, most people won't/can't do the work to fact check everything since there's too much info and truly verifying everything would be a monumental task.