They have far, far, far, far less power to edit and censor the views that are put forth through them than any media distribution platform known in the history of the human race. Not only that, they've chosen that very hands-off editorial policy as part of their way to grow both contributions and eyeballs exponentially.
This argument is quite literally 180 degrees wrong.
The reason they have such a hands off approach is because they want to be recognised as distributors, not publishers, in case section 230 gets revoked and internet publishers become responsible for the defamation on their sites.
This is the great irony of Trump's war with twitter, where he keeps threatening to kill section 230 so people can't say mean things about him, but if he did, Twitter would have to remove almost every tweet he's ever made.