If I may chime in, that's actually a very good question, though it's not what this thread is focused on.

There is, in the Western World, right now, an ongoing debate about that exact question. Evil, if you look up the definition, is the deliberate doing of something that is profoundly wrong, by someone in a position to appreciate the wrongness. That something is "wrong" is a moral judgement, and people disagree to varying extents about what is "wrong." Pretty much everyone agrees that banging an old lady over the head and taking her pocketbook is wrong. There is no such consensus about the moral status of administering capital punishment. And so there is an ongoing debate.

In Western Europe, capital punishment has been discontinued. The majority of people in that part of the world feel that it is wrong. Same thing in Mexico. (This is why the Mexican government won't extradite to the U.S. persons wanted for crimes that incur the death penalty.) But, here in the USA, that issue is still up for discussion. Some people think capital punishment is evil. Some don't. Quite a hefty percentage of Americans think that capital punisment is a good and worthy tool for advancing the cause of justice. People hold differing ideas about it.

People hold different ideas because people differ in their experiences and in the influences that they are exposed to.