I believe reddit has been a part although its hard to say how big of ones it’s played in further diving people. It’s in my experience the worst social media at putting you inside a completely one sided bubble with twitter as a very close second.

Part of that being downvote is just used as i disagree with you even when you are adding a valid but different view to the conversation. I don’t use reddit anymore outside of trying to find recommendations for products but even that is being gamed now.