None of us are entirely good, so we all do a little evil now and then. Dammit. When I do this, I repent, try to fill myself with more of the Good and hopefully the spaces for the sin get smaller and my access to the Good gets bigger.
Some evil doers have very little of the Good in them. Anything we can do to have them partake in the Good improves them.
Justice is good. If we can mete out justice to them, the evildoer partakes in the Good and is made less evil.
Sometimes the noose improves people and brings them closer to the Good.