I think you make a good point there, and it's something that always bothered me about the typical left-right or urban-rural or facebook-echo-chamber explanation

I think you make a good point there, and it's something that always bothered me about the typical left-right or urban-rural or facebook-echo-chamber explanation. I do think all these things play a role, but as you say, it's not like we lived in wonderful diversity before these things. Personally I think what changed, and the article does a good job highlighting that (which made it refreshing to me), is that the degree of our diversity (or lack thereof) has changed. In the army, or college, or church, you're forced to become close (or at least get to know somewhat intimately) many people who are potentially very different from yourself, lottery-style. There's a whole spectrum between that and the 'bubble' many of us live in these days (in part caused by the internet). There has always been segregation, we've always had a preference for friends and social groups that are relatively 'close' to us in various aspects. What changed, perhaps, is that we now have to luxury of avoiding 'others' almost entirely, where in past, through church and army and so on, we had to have meaningful (if not close) relationships to those 'others'.