Certainly the ability to kill should not be entrusted to governments. I agree with you there. Power corrupts, and when people in power are given the means to kill they abuse it.

But the way I see it, a community killing a killer is a collective act of self-defense. If I had to kill somebody to keep them from killing me, I would do it.

Obviously something has to be done about the murderers. No matter what you decide to do to them, be it killing them or confining them in a small and unpleasant place, it would be a "crime" to commit that act upon an innocent person. But murderers are different and need to be held up to different standards.