limits to growth and equity in social network communities?

An urban planning problem emerging in social-networking sites?

Social networking researcher dana boyd suggests in her recent blog entry that facebook opening its doors to everyone is problematic, that social networking sites can't sustain "conflicting social contexts": http://www.zephoria.org/thoughts/archive...

Facebook used to be only available to those with .edu, high school, and corporate email addresses; now it's open to all.

So I ask:

If an all-access facebook will ruin its sacred purity, does this propose that a limits to growth exists in social networking communities?

Does exclusivity define place?

Do borders define contexts?

If different and "conflicting social contexts" (students, non-students, and as danah puts it, those "obsessed with youth - parents, authorities, pedophiles, commercial enterprises") are able to live within the same networked community, do they have to be separated into different (virtual) neighborhood quartiers?

Is it okay for everyone to potentially mingle like in a real city or ideal agora? or, are enclaves the answer?

And are population levels, and one's origins, related to the "quality of life" for a real urban or virtual cyberspace place?