Facebook is making this easier because it makes keeping with touch and finding people easier. But Facebook is only an incremental step forward here; the objection you're raising should be aimed at the entire Internet. It's the Internet that lets crazies find each other and organize; before Facebook, it was other sites, other services.

I'd go one step further - that's just consequence of better communication. You can't have one without the other. If you make life easier for everyone, you're also making life easier for the crazies, and for the bad guys. Personally, I'd still say it's worth it.