kind of the million dollar question, isn't it? I don't think there's an easy answer. I think the fact that eventually all communities homogenize and die gives most community planners ample reason to study the issue. That said, I think if you look at the differences between a geographic community and an internet community, the biggest difference is friction. If your community is "Sedona" you had to move there. You had to sign up for electricity, phone, television, internet, garbage service. You found the restaurants, you found your favorite parks, you found the speedtraps. If your community is "Reddit"....
If your community is Sedona, your neighbors might annoy you but you shop at the same grocery store, you stop at the same stop signs, you vote in the same elections, the same rain falls on you all. Loudmouths are bitched about around the dinner table, not the commons. Everyone just wants to get along and enjoy the community. You're all invested in it, economically, socially, emotionally. If your community is Reddit... This is part of what the points systems endemic to internet communities attempt to curb. They are "investment." However, they're not the same "investment" as "I can't move because I really like the Thai food down the street." What you need is something "sticky" to cause people to do things they don't want to do in places they don't want to leave. You need things to be difficult to set up and difficult to break down (ever tried to leave Facebook?) You need a social structure that causes people who don't agree and won't agree to somehow have to agree in order to participate in the commons. The problem most internet communities face is their emphasis on fluidity, on ease, on transactional utility. Most real communities emphasize those things that cannot leave their community (parks, shops, restaurants, scenery). You're "stuck there" and have to deal with people's bullshit. Of course, it's generally something other than "people's bullshit" that attracted you in the first place. With online communities, it's all about the bullshit. And since it's so easy to come and go, the only people left after a while are the bullshitters. The trick, then, is to add some sort of inherent value that emphasizes transactional friction - aka politeness, opposing viewpoints, etc. And I have no idea how to accomplish that.
As I see it, part of the problem with most aggregator communities is that they lack context. It's easy to be a dick because you don't have to see the person your being a dick to ever again. This is why the emphasis on following users exists on Hubski. Through repeated interactions a context begins to form between users. eventually, in some cases this context can be governed by mutual respect and even friendship. You have skin in the game because while you have an anonymous username you have context and an equity of good will built in to that name. I don't want to start-over in another community and not because of fake internet points but because I've amassed relationships here which can provide a context around discussions on multiple topics. Protecting this as we scale becomes the priority IMO. I often say that structurally we are far more like twitter in some ways than we are reddit. -on my phone so apologies for any errors.
I'd usually heard the echo chamber described as more local than all of reddit: it's /r/conspiracy+alexjones+moonlanding, /r/liberalism+antigmos+politics, /r/guns+conservatism+alabama, /r/sanfrancisco+startups+paulgraham. The counter to that is +random, +bestof (In theory), and +news (In theory). At hubski, /r/guns becomes #guns, but mk is much more complex, and the hope is that mk + kleinbl00 + OftenBen ends up as a union of #economics + #selfdefense + #foodforthought + #filmindustry + #altgov.