propagandistic control

AT&T was a government-created monopoly that not only directly prevented (not indirectly, via hand-wavy causal chains) the emergence of competitors to its monopoly, but even directly suppressed the emergence of competitive collateral markets that relied on telephony services.

Monopolies aren't bad in themselves. Both common sense and the law require that monopolies be broken up only when abused. And you need to be concrete about the market and the abuses. Every business enjoys some kind of monopoly in some dimensions because our economy is finite, not to mention time and geography. If you went around destroying monopolies you'd be breaking up companies left and right all day long.

Of all things to care about, supposed monopolies in social media are the last the thing people should care about. The rise of Breitbart is all the proof you need that there's nothing to "fix". You don't breakup companies because you want a particular outcome or merely dislike the status quo; it's foolhardy to think you can engineer a particular outcome, and foolhardy to even want to try.

The closest parallel to historic breakups would be Google, given it's dominance of online advertising. But while they throw their weight around, AFAIU there's hasn't been any substantial abuse (or even credible accusations of substantial abuse). Probably because while dominant, they don't actually hold a monopoly or participate in an oligopoly that has the capability to close-off access to the market to newcomers.

People seem to care about supposed social media monopolies because of the bike shed effect. Everybody uses Facebook and Twitter (except some of us), and so everybody has an opinion and believes they're capable of making an informed judgment call. That's the worse way to drive policy.