I hear you, but respectfully disagree.
Firstly, the irony of posting "step outside the echo chamber [my emphasis]" on somewhere like MN is hilarious, but we'll leave that aside for now.
I can't speak for Reddit as I don't look at it, so obviously your experience with it trumps mine, but I would like to focus in on your assertion that MN allows for all sides of an argument. I don't think that's true.
I think MN, and most of its posters, would like to think that - I really do - but the facts speak for themselves.
We have thread after thread after thread where posters who raise their heads above the parapet and suggest anything that goes against the close-minded group-think that pervades here in such abundance are immediately singled out, jumped on, and attacked. There is rarely, if ever, a concerted effort to consider what that poster might be saying, or to understand it. Arguably, that skill is essential to any functional, grown-up society.
Obviously, not all MN posters are cut from the same cloth, but I don't think anyone can truly - hand on heart - say there isn't an ugly, rabid, anti-trans and pro-GC sentiment here that is truly despicable.