In fact, we humans already form a decent system for weeding out bad ideas/opinions, we just don't listen to our own past experiences on the matter. We found out that fascism is putrid and yet now we try to come up with a new system that will weed it out instead of just chucking it into the garbage bin and moving on.
It's not paternalistic or a dismal view of humanity or that "humanity cannot be trusted with such a dangerous idea", it's because the people advocating for it constantly lie about it and intentionally trick/indoctrinate others into following. Under the right circumstances of me growing up, I fully believe someone could have deceived me into believing it, so I don't think I'm better than anybody who got sucked in. We can trust in democracy as long as we take proper precaution against things that prey on the freedom of expression and association in order to remove those rights from others.
Put another way, what real benefit is there to "freedom of speech, except for advocating fascism" as opposed to "freedom of speech, no exceptions"? The US already doesn't have pure unrestricted free speech because there are exceptions made for outlier situations where free speech is not protected in efforts to secure the safety of others. That hasn't led to total collapse or censorship.
Personally, I feel there should be legal protections for all speech, but not protections from social ramifications. By this logic, I am totally fine with the idea of punching fascists. Which itself could be hit with assault charges, but then, how many juries would disagree with the reasoning for the violence? Let the masses decide for themselves, basically. It's what bothered me about the firing of James Gunn and Roseanne both despite their polar opposite politics. The companies that employed them cared so much about what the public thinks or feels that they couldn't be bothered to let the public decide for themselves to support either celeb or not. (And I know Gunn has since been rehired, but this happens so often, my point stands.)
I lean towards anarcho-communism myself, generally close to the original communist definition of libertarianism. So my answer to which authority should run things is "none". Facebook runs their own ship and are free to choose which content they will platform. While I would prefer a complete absence of hierarchy in all aspects of life, I think we can agree that this is probably not going to happen at FB.
I also strongly support anarchistic deplatforming and generally hindering fascists, nazis, racists and other bigots from spreading their noxious views. We have to realize at some point that some views simply aren't worth spreading.
And somewhat related, does this mean you have as dismal a view of humanity as it seems, that you don't want people exposed to dangerous ideas? This all seems necessarily paternalistic. EDIT I can't imagine, for instance, trusting in democracy with such a view.