But it is black and white: kill or not. My intentions are neither good nor bad, they are what they are. I don't kill. And your contention was that economics were the deciding factor, virtue wise
Economics was only one of the two main reasons. The other one is that I think killing them is doing them a favor. A wretched, miserable, haunted, perhaps hideously corrupted and evil life is something I don't want anyone to experience.
Aside from that, your saying it is black and white. Kill or not. Well, if you don't kill them, it could potentially cost a million dollars. What if instead of paying the million dollars for the murderer we invest in schools, hospitals, welfare, worker training programs - all of which would help a lot of people. Some peoples lives might be saved. Other people would be able to better support their families, maybe afford to send their kids to university. Not so white and black anymore, is it? Economics is a much more important aspect of the problem than you might realize. You can change a lot of lives with a million bucks, maybe even save some lives.
So if it is such a mercy, why provide it?
Because mercy is a virtue. The murderer may be a monster, but we aren't. Torturing the murderer by keeping him alive so that the misery, pain and guilt he has inside cause him massive suffering is evil.
You must agree that the motive of the mercy killing of a killer by those who already advocate killing the killer sounds a mite suspicious.
I don't understand what you said here.