This is how it works in all fields. We can’t talk about different possible climate scenarios because of denialists. We can’t talk about issues with evolutionary theory because of creationists. We can’t talk about genetics and intelligence because of racists. We can’t talk rationally about fringe ideas like UFOs or psi because of new age wackos and cultists.
The best way to shut down rational discussion in an area is to promote sensational lunacy. Then everyone self censors to avoid sanctioning the lunatics. This is not entirely irrational… many of the nuts in question are really toxic and dangerous. Things like racism and antivax hysteria kill people.
Most of that stuff is grassroots, but it could certainly be weaponized. For example if I were a pharma company and wanted to cover up a problem with a vaccine I would promote hysterical antivax bullshit. That way you make it impossible to rationally discuss problems with vaccines. If I were running a child trafficking operation I would promote Qanon.
This phenomenon is not new per se but social media renders it devastatingly powerful today.
I don’t see a good solution. Every solution is either “let society be overrun by cults of idiots” or “implement some kind of exclusionary elitism or totalitarianism.”
Maybe the solution is for some well meaning person to purchase and erase Facebook and YouTube. That would at least render the problem less acute.