I think an important distinction with Reddit compared to Facebook, is that AFAIK Reddit doesn't target you as an individual with subreddits they think you might like, and show you an echo chamber of information on /r/all that fits your views.

For example a gun fanatic viewing Reddit, won't just have gun positive stuff on his /r/all, and other stuff that fits his view. You have to know about a sub, to be able to see it (except the big ones that show up on All, which is pretty harmless topics), while on Facebook you like one post and suddenly you're fed stuff you never seen or even thought about before and it's not long before your feed is completely different from anyone else and filled with stuff to reinforce your beliefs.