I'm an old fart and pretty strict about not stealing and see no problem with removing a few fingers of those perps who do get caught as well as their drivers. You have to admit, it would be a helluva deterrent.
Much as I like the idea of some "street justice" too, the courts don't see it the same way and you'd be charged criminally with setting a trap, and then the fingerless dirtball would sue you in civil court too and likely collect.