While that may be true.. do you not believe that the exceptional openness of either of those two platforms has an impact on places outside of them? Do you think there's no intangible benefits to you by these places merely existing?
I have yet to hear a positive argument for their existence, and "well it collects the dirtbags!" is actually not one. I spent years tracking reactionary and fascist movements on the internet and how they interrelate and spread information; these sites more or less exist to do exactly that. The targeted harassment campagins that target random people they've decided not to like--that's just "for the lulz".
Oh, there's definitely an impact.
> Do you think there's no intangible benefits to you by these places merely existing?
Yeah, the campaigns to harass a game emulator developer to suicide because "40% is a good start" are a fantastic benefit to society, obviously.
So the "just create your own platform" trope has be tried and failed.
But I think you'd find two problems: determining what could be illegal is really hard (what's a "true threat" and what's a tasteless joke?), and also you'd end up with a community that looks a lot like 4chan or parler. Not a place I would choose to hang out.