Instant Karma

Part of the concept of human civilization is that you just don't go running around killing people. In fact, what distinguishes a human civilization from a bunch of monkeys standing around in a cage is the concept that you are accepting civilization's offer of protection in exchange for the promise to not go around killing people.

There are exceptions to this that arise, should you encounter an exceptional scenario like someone trying to kill you. Even then, society doesn't say "Oh, it's okay to kill him, then." Rather, we concede that you may use sufficiently urgent and violent force to immediately stop him from his attempt, and if he dies, he dies.

This is why setting booby traps is illegal. The very fact that the device is designed to deploy lethal force in the absence of a human operator means that the one key factor that warrants the use of lethal force is not present. If your self ain't there, it is ipso facto not "self defense".

Too bad the dude in Maine who whacked himself with his own booby trap on Thanksgiving Day hadn't thought this through.
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