You're right that it is too simple, but it's an easy rule of thumb with which to think about and frame the problem. If it's illegal to kill a human being, then

You're right that it is too simple, but it's an easy rule of thumb with which to think about and frame the problem. If it's illegal to kill a human being, then it's illegal. The existence of a death penalty where the state is able to do it in certain cases, as in the main case where someone themselves has broken the rule and murdered, for me, still does not justify any kind of legalistic justification for sanctioning they be killed. While "the state" is this abstract entity formed by all of us, the state has to act through people, who then have to be involved in taking a life. The state's premeditation of the killing of the murderer is even more premeditated and drawn out form of murder. It's easy to be blinded by the language used around this towards what is happening. I believe even further that if the state is allowed to do it, it opens a loophole in thought that could actually cause more murders to happen, because if the state can do it, then maybe I'll do it too...