Communities have been eroded, not by the Internet, but by television which locks us into passive, isolated cubicles and bombards us with content, most of which is explicitly designed to encourage consumerism, passivity and superficiality; by suburbanization that isolates families from each other, from work, and from the world; and by the increasingly stressful and long work hours which leave very little time for anything else.
In this regard, the Internet is the greatest antidote to anti-communitarian forces. Frankly, I find even the most mindless lolcat sites on the Internet to be an improvement over canned-laughter-filled sitcoms. The point of lolcats is not the lolcats themselves, but to share them with friends, comment on them, make more of them, and enter the community via the joke. It's the community, not the cat, that matters. (If you doubt this, try selling a book of lolcats and see how well it does.) I write this review in the aftermath of an atrocity; the assassination attempt in Arizona on a Congresswoman that claimed the lives of six others including a child. Every Internet community I am part of is roiled and there is widespread discussion on most of them about the event. Fifteen years ago, we'd all be watching TV, not communicating with each other.
Tip of the hat to CameronCRussell for the link tho this great book review. I'm gonna pick up (and by that I mean download) a copy.