Oh, and Buster, in Europe these things don't spit out tags. You got a bag, get thee to a desk for a tag - where excess charges can be charged. As for security - if I did happen to be a nasty, and someone said, 'Hey mac, got a knife?' you think I'd answer in the affirmative? That, old son, is what those funny rectanglar things you walk through and those big machines you put your carry-on stuff through are supposed to detect... And they do the passport/ID check at the gate, no matter where you got your boarding pass.
As for 'faking a tag' and getting a bomb on board, well you'd have to be pretty good at faking bar-codes, since that's how the bags are sent to the right flight. In any case, the old match-the-bag-with-the-punter process ensures that all bags have owners. Nothing will stop a suicide bomber putting a bomb in his bag & getting on the flight but your apparent scenario of a 'fake' tag and no punter getting on is a non-starter.
Self-check-in machines don't 'give control to the punter', they allow you to get the a/c away on time and not miss your slot, by helping get us annoying full-fare punters onto the bird in nice time. in any case, what is the problem with the punters having a bit of control? We're human, too...