Forget "inherently" good or bad. It's entirely possible that the guy in the vest isn't a morally horrible person; he may have been brainwashed since birth and genuinely believe that his actions will bring about a better world. Still, he intends to kill himself and as many other people as possible, and if I have the ability to cause the only death to be his, I'm doing that every time.
I understand the self defense argument. Law Enforcement and Armies are trained to respond with violence to people with intent to kill. The passengers of United Airlines Flight 93 are heros.
Killing "bad people" to save "good people" is not a self defense argument. The statement is too general. Is it okay to do medical testing on criminals if it speeds the advancement of medicines that saves law abiding citizens lives? We could have limits to only use people found guilty of the worst crimes and increase the legal burden of proof for criminals going into the medical testing program. It would decrease overall harm. It would kill bad guys to save good guys. Still, this practice is illegal for good reason. We need a better reason to kill someone than they are bad.
