Only about a quarter of the world's countries have the death penalty so even if "many people believe that's a good example of killing other humans", most do not. While I abhor the nature of privatised healthcare in the US, I think judging—and, certainly, killing—people based on potential indirect harm they've caused is a very slippery slope.
I don’t know of a single country without a military nor a country that doesn’t allow law enforcement to use lethal force. So your statement that most people don’t think they are valid examples of a good killing of someone is disingenuous.
But my point was about justice and if we think there is a point someone deserves to die. If we say there is, which I think it’s clear, there is. The whole question about people being happy is about them being happy that they‘re seeing justice. But you tried to side step that.
Also, on the death penalty, I don’t think it’s ever gone to a vote where the people decided. So saying most people are againist the death penalty sounds hollow.
