I've seen this argument so many times. I like something, so we have to make a law to force it to exist. Or, I don't like something, so we have to make a law to make it illegal.
Unless there is a monopoly, and social networks certainly aren't one, there's no reason to force them to do anything.
So why are we forcing social networks to do a lot of things already today: We force them to remove illegal content, remove content that is not suited for minors, moderate content that is traumatic, protect people's privacy etc?
I don't really understand? Is your point that we should not be doing this as well? Is your fear that the state of California will moderate Twitter?