If murder is illegal, then it makes no difference if the state does it as punishment for committing murder. You’ve still sanctioned a murder, admittedly of a murderer. A civilised country accepts this simple logic and doesn’t sanction murder under any circumstances.
No. Murder is not the same as killing, just like not all taking is stealing. Even the most civilised society imaginable admits that killing is sometimes acceptable (in self defense, for example). Killing done by the state is trivially not murder by definition, and less trivially there are justifications you can argue about. But you have to argue about it, your "simple logic" is unfortunately too simple.
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...
By this logic, holding someone against their will is illegal too. When a state does it, we call it incarceration. Is it wrong for the state to sanction incarcerating someone?
This goes much further into philosophy, politics, and legality than I'm comfortable with but there's lawful and unlawful killing, the difference being... well, one is allowed and the other isn't, as per the law (be it national or e.g. international / warfare laws).
I can't even make a statement whether killing is always morally injustifiable or not.
I love the moral direction, but this sadly doesn’t hold up to philosophical scrutiny. Is it murder to
1. Kill someone who’s about to kill someone?
2. Kill someone in a defensive war to defend your freedoms?
3. Kill someone by prioritizing things other than their medical care, eg in hospice?
4. Kill someone by letting them smoke/drink/overeat?
5. Kill someone by letting them starve?
If you want to say that no country is civilized yet then hey I’m with ya. Otherwise, it’s not quite so simple. The death penalty is a tragic injustice, I agree, but just saying “it’s murder” is not a serious engagement with the issue IMO.
