If someone posts a pirated copy of a movie, Facebook is obviously not responsible for piracy. That's on the individual. If Facebook promoted the post, did something so that a million people saw it instead of a few hundred then that amplification is something they should be held responsible for. The vocabulary of legal and ethical models of previous xcommunication technology doesn't fully apply to social media.
We need laws to specifically call out the misuses of social media algorithms and control systems. We already have a good framework for the content of speech, so allowing "whatever is federally legal" seems to me to be a reasonable constraint on platforms, with a reasonably defined minimum level of user distribution control (you can post to people that subscribe to your feed, but the platform doesn't have to index or make your content discoverable, maybe. ) Curation and manipulation of content beyond what the user is responsible for seems a reasonable line for liability, to me.
The societal problem is the amplified negative interactions, creating feedback loops of doom and dissension.
Then again, decentralization and federation kicks a lot of these issues to the curb, so maybe the next generation of social platforms will get rid of the issues for us.
Facebook has specifically designated itself as a platform, not a content provider. IF what you are saying is true, we need to remove Section 230 protection and force Facebook to be accountable for all of its content.
Personally I think there are countless alternatives to Facebook and trying to nationalize into a utility, or regulate it with an agency will only serve to foment authoritarianism.