That's exactly what "reining in" looks like. Instead of being an alternative to, e.g. the New York Times and opposing the next Iraq war, social media just becomes yet another rah-rah cheerleading mouthpiece of whatever opinion the "serious people" hold.

I don't know if you consider Chomsky to be a "serious person", but Manufacturing Consent does go into how the people actually in charge of the government (professional civil servants, corporate lobbyists, etc) manage to make it seem as if their opinions are infallibly correct and countervailing opinions are thinly veiled crankery. What social media did (at least in its early days) was give everyone the ability to manufacture consent at a scale that previously was only the domain of the large media corporations. The establishment media is obviously threatened by this and are working to ensure that the new media follows the same guidelines as the old, even if that means censorship.

Of course, that's not how the establishment media phrases it (and probably not even how they believe it). They see it as "protecting" the people from unsavory "Russian fake news". In reality, though, that's just a lie they tell themselves and tell us to justify their continued hold on the ability to decide which opinions can be held by "right-thinking people". If they were truly interested in "the marketplace of ideas", they wouldn't be pushing so hard to make platforms as centralized, controllable and censorship friendly as they are.