I'd be the last one denying anyone the right to defend themselves. Heck, that's one of the things I absolutely hate about living in Europe (well, that, and the absurd taxes).
In Holland, it used to be pretty common for people who defended themselves against a burglar to be sued by the burglar, to the extent where police officers would (unofficially) advise you just to toss the burglar outside rather than keep him inside your own house, and risk finding yourself sitting in jail for assault while the burglar would be let loose almost the same day.
Luckily that is now starting to change, but self defense, according to Dutch law, still stops at the point where the direct threat is negated. Go beyond that level, and you'll enter the realm of excessive violence. There's huge gray areas in there, as it is entirely possible for even a single hit to have unintentional consequences and what not, but still. I am not convinced 12 stabs is neccessary purely from a textbook definition of self-defense.
That said, I still am on the side of the kid who got bullied and ended up pulling a knife. I merely am having some trouble with the judge labeling it self-defense.