Just look at Faith. If she hadn't had a Watcher, she would have been even more out-of-control. As it is, she was already running around killing people willy-nilly and working for evil folks as "muscle".
And now there are all these sudden Slayers (and, again, I wonder if it stops at a certain age or continues on to include all these disillusioned women who really want to pummel their ex-husbands and suchlike) who have no idea why they are so strong and fast and whatnot, and have nobody guiding them in how to channel this new power. Can you say "potential girl gang"?
Hmm. How come no one but me worries about this sort of stuff? I think it would be really funny if next season on "Angel" he and his crew spent a large percentage of their time fighting new Slayers and cursing Willow for Slayerifying them all. Heh.
I'm just sayin'.