It's not social media, it's the internet. Whether on Facebook or reddit or Twitter, you can find a group of people who reinforce whatever bad ideas you have. This creates echo chambers wherever you go. If you think the world is flat or run by the illuminati you can find 10000 people to reinforce that belief. But it's also great to be able to find communities for whatever niche hobby you might have , and it's spreading real knowledge faster than ever in history.