If you are liberal, you mix with others who are much the same
And if you have views that are to the left or right of the main, you tend to hear similar views so your own view is reinforced as 'typical'.
I've said so much of this stuff before. But MN is probably a big echo chamber as well - it's really hard constantly debating the same stuff and constantly repeating the same arguments and it can get heated. But if you step away and don't engage, people start listening to different voices and views go unchallenged.
It's now becoming more real.