But do we have a responsibility to not hinder someone else's free speech? Not with regards to the current post but just thinking in lines with what you said.
Yes we do, but we do not have an obligation to facilitate it. Private forums have no obligation to publish or distribute anything they don’t want to. Their owners and operators have rights too. Free speech simply doesn’t apply. Just go and communicate somewhere else, or build your own chat service, or publish a leaflet or book, or whatever. But I have no obligation to allow you to come into my house or business and say these things.
I don’t think it’s possible to mandatorily restrict editorialising without killing platforms. Any such restrictions would be a spammers, griefers and pornographers manifesto. Restricting editorial rights is a horrible can or worms to open.
But anyway, there are no social media monopolies. We have Twitter, Facebook, YouTube, Instagram, WhatsApp, iMessage, Discord, Signal, etc, etc, and it goes on and on. They’re also very segmented, Facebook is huge but it’s almost irrelevant to kids and young adults. New services pop up regularly because barriers to entry are incredibly low and segmentation is so high.