I think tumblr excels because, lacking a front page like reddit, the user's that hate each other never interact. And I'm increasingly sure that this is the only method for obtaining non-dysfunctional societies online- non-overlapping tribes of users. Why should the subscribers of /r/stormfront try to coexist with /r/BlackLivesMatter? It's like trying to house wolves and sheep in the same pen. Give each their own echo chamber.