It is, perhaps, the best option to assume that Facebook, Twitter, YouTube, etc. aren't neutral platforms.
Indeed, even when people assume they're neutral, that assumption doesn't extend to full laissez-faire. All these platforms have basic "censorship" in place for legal compliance (DMCA takedown processes, interactions with government anti-crime systems, a need to follow US law regarding dissemination of pedophilic content, etc.).
Indeed, there are legal obligations and such but, perhaps, the problem is that not all people assume social platforms are neutral in the way they do other media outlets?
Maybe because one can have extreme political views and easily find other like-minded people then one can become somewhat blinkered? If one's platform of choice is also stifling some content there is still enough of other stuff around that one may not notice?
Indeed, even when people assume they're neutral, that assumption doesn't extend to full laissez-faire. All these platforms have basic "censorship" in place for legal compliance (DMCA takedown processes, interactions with government anti-crime systems, a need to follow US law regarding dissemination of pedophilic content, etc.).