I think social media brings us closer together with persons who are more like us than with those who are not like us. In other words, with social media we can talk to persons from anywhere in the world, so long as they speak our language. With Facebook, if you're willing to use the translate feature - you can go further still and talk with persons who speak any language at all. They would only have to also be willing to use the translate feature, and then the translations would have to be sufficiently good for proper communication to take place.
But we all tend to really just want to talk with persons who think the way we do about things, and feel the way we do about those things too. So really, social media just allows us to find like minded individuals from long distances away. Social media brings us together with like minded persons, and maybe from there groups of like minded persons drive themselves further from groups of persons with unlike minds.