The 'dimwits' was not intended for you - I apologise for the misunderstanding. It was rather a reference to some of our laws which were in fact written by emotional dimwits (and also accepted by such a lot).
I think we need to distinguish between the two situations: whether someone is facing an immediate threat or not. The first situation really may come down to kill or be killed. This applies not only to war or 'war on terrorism' but also to ordinary criminal acts. There is nothing wrong with it and the concept of law does apply here.
In the second situation, when you encounter someone who intends to cause harm on you, your country or whatever but at the very moment does not pose a threat, then there is absolutely no reason to execute such a subject. Doing so would be unlawful and must be prosecuted (drumhead court-martials should belong to a hopefully never recurring past).
I do believe that we cannot maintain a credible state of law as long as we tolerate and even encourage behaviour outside our concept of law no matter who the subject concerned is.
Again, I ask you: where do you draw the line? Quite a lot a people I've met are at least in parts irrational. Shoot 'em all? Or 'literal animals' only? (Btw, to entitle someone as an animal or something other not human is a common first step to the most inhumane treatment...)