I agree with you in feeling that instead of isolating you, the internet connects you on a very personal level with people who have the same interests. I don't know anyone in RL who is a fan of anything, let alone Buffy, or has an LJ, and that would make it pretty lonely if there wasn't the Buffy fan community.
And writing fanfic? Well, it's vampire porn, nuff said - I have mentioned writing to some people, and their horrified reactions, as if I was completely insane, taught me to keep this silent in the future.