I think the center issue is having something in common, which binds people together.
Once they get over that initial little hump it becomes friendly instead of just mandatory, but it takes that push.
How often do you make friends with complete strangers with whom you have nothing in common (that you know)?
Yeah, the Mormon in the other thread (hi) seems to be suggest that their supernatural belief system is integral to their social system, and that's a hard claim to disprove--the LDS church is possibly the densest store of social capital on the planet.
That being said, I believe there are other belief systems capable of inspiring these connections, overcoming them. There have to be, since they're all based in the nervous system. And, of course, if you're a Mormon, none of the "crazy stuff" is, ontologically speaking, supernatural. It's part of nature.
What does "a structure community" look like? I mean, how would you recognize one when you saw it.