I'd like to hear more about why it would be a moral failing to moderate content without assuming liability. If this were codified into law it would on a practical level eliminate the possibility of moderation in many cases. That feels like a net loss to me, since I'd like to remain able to visit online spaces with the expectation that I won't be served certain kinds of content (hate speech, animal slaughtering, smaller things like political positions I find objectionable after I've had a hard day and just want to relax, whatever).
That doesn't mean it's moral, I suppose, but it feels like an uphill battle to prove that it's not. What are the harms that derive from allowing platforms to moderate without assuming liability? What's the alternative? Either they lock down everything and have human moderators approve all speech submitted to the platform, which seems draconian and expensive, or they let everything through, which reduces the usefulness of the platform and forces them to host evil content or content that may cause more harm than good (e.g. medical disinformation). Either one seems worse than allowing moderation while waiving liability.
Further, this flies in the face of moral custom. Although there can be legal penalties under some scenarios, we generally don't find people very much at fault for illegal acts that take place in spaces they control unless they had knowledge of or participated in those acts. If my fiancee starts dealing drugs out of my house, and keeps it secret to me, I shouldn't be on the hook for that. And yet I can choose to "moderate" who does or does not live in my house.
What's different here? Facebook owns the space, would prefer not to serve hate speech, and 99.9% of its users would prefer not to be served hate speech. What's the harm? What moral principle should prevent them from doing so?
Finally, what about sub-platforms moderated by users? Can reddit morally allow subreddits to moderate? If they can't, so much the worse; but if they can how is that different in principle from reddit doing the moderating?