Go back 100 years and just because people had more shared media, it didn't make everyone think the same. There were communists and fascists, people or loved or hated new technology, music, etc.

Historians reading newspapers learn what a small part of society thought, and hopefully read them in the context of as much other information from the time. But maybe the newspaper made something that hardly anyone really cared about seem like the main opinion, or vice versa - it happens now days, likely more back then.

If anything social media might make things easier for future historians, with literally billions of opinions written by everyone from homeless people to billionaire CEOs, all within large datasets to be analysed.

More importantly though is the amount of semi-political & marketing-related polling that goes on. By semi-political I mean things politicians want to know, rather than polling about politics - people regularly get polled on anything from transport ideas to favourite songs. And I imagine that's a huge trove of data compared to what there is around public opinion even decades ago, yet alone centuries.

The divisions we had were already bad enough. Now amplify those up to eleven with social media, and you end up with the perfect tool to endlessly divide society in difficult to detect ways. People seemed to be at least somewhat aware what the doctrines of the various -isms were, even if warped through propaganda. Customized echo chambers can make it impossible for any affected slice of the population to ever experience how deep in they really are, and get a genuine impression of what people outside are like and what they think. Best case, they are seen as ignorant, worst case as a danger, which can lead to violence being seen as a legitimatd tool to deal with them. We have seen what this can lead to on Jan 6, 2021.

On the contrary, the one social medium that puts everyone in a shared, global space rather than customized "echo chambers" (twitter) causes more trouble than the rest of them put together, not least your own example.

> In a corner of the large room a chime sounded and a tinkling mechanical voice called, "I'm your free homeopape machine, a service supplied exclusively by all the fine Rootes hotels throughout Earth and the colonies. Simply dial the classification of news that you wish, and in a matter of seconds I'll speedily provide you with a fresh, up-to-the-minute homeopape tailored to your individual requirements; and, let me repeat, at no cost to you!"

Ubik, by Philip K. Dick

Social media, if it were a physical store, would be endless aisles of dopamine inducing pictures and information.