It's the publisher vs platform debate. If you're curating content based off of promoting your company's vision of acceptable free speech, then you become a publisher and a whole different set of rules apply to you. You're liable for much more in the eyes of the law.

You can't cherry pick the advantages of both and hide under the guise of being an open platform.

If you want to take that tactic it's probably just better to reframe the argument.

Most of the problems that come from being a massive social media juggernaut like facebook/twitter/etc come from those services being free.

Being free is what makes them massive monopolies and gives them such broad reach. I think 99% of the problem cases AND the lack of competition in the market could be plugged by breaking the ad-supported/VC-supported model and forcing these companies to charge something to their customers.