Freedom of speech is not protected by the constitution on social media platforms and, frankly, I don't want 100% free speech on social media.
Take a look at HN. HN mods do a brilliant job of moderating. We don't have 100% free speech here and the platform is better for it. The discussions here tend to be much higher quality than on similar platforms like Reddit. That's probably a big reason why you're here reading this comment thread.
However... I've noticed a difference between HN and the likes of Facebook or Twitter. As far as I can tell, HN mods focus more on how you say something rather than what you say. If you're civil, respectful, and on-topic you're seemingly allowed to present just about any idea.
Meanwhile, most other social media platforms seem content to let other people be complete pricks to eachother as long as they don't present any ideas which the platform have decided are wrong or "dangerous".
I think the HN moderation strategy makes for a much better platform. I'd rather talk with a respectful person who I disagree with than a jerk with whome I agree.