What test do you propose, other than self-identification, that would cut across every possible definition of "hacker"?
This is how Livejournal used to work, and it resulted in everyone knowing at least one other person, which was important for a community site.
And this didn't cripple the growth of Livejournal at all. You only get one invite a year, but you get it immediately on joining. I invite you, you turn around immediately and invite someone else, who invites someone else, etc. The 1/year rule is meant to make me careful about who I spend my one invite on.
most of the annoying 14-year-olds wouldn't be our friends
That's definitely the case here. :)