I'm not sure exactly what makes them different from more focused forums, but it's something and – in my opinion – I don't think it's a net good for society.
Personally, I have no account with these services. I used to but I deleted all of them and it's made my life richer, not poorer.
Have you ever been on a smaller focused forum without mods or rules? I haven’t.
Pornhub (based in Canada) recently decided to allow uploads only from verified accounts due to political pressure. Twitter/Fb could also require ID verification, for example. They basically already do (require a cell number after account creation), but it's not enforced in all countries.
Anyway, no magic bullet, but if they are held accountable, they will find solutions pretty quickly, as Pornhub did.