"Evil" always depends on where you stand, even when it involves killing people.
If somebody attacks you or someone you love and all you can do is killing the attacker to prevent them from killing you or someone you love, is that evil?
Is it evil when somebody is terminally ill, and requests to die in order to be spared from further suffering, is it evil to kill such a person?
Is it evil when somebody brings you beyond any level of insanity making you unable to control yourself going berserk killing the one responsible in the process?
The latter is already a hard one, but doing something you are not supposed to do is not per definition "evil". Many people who did commit a kill in that situation regretted it immediately after, something an "evil" person would never do.
The #2 situation is already open for debate. Some people would deem you a hero, others would deem you a criminal or even compare you to the nazi regime for that (if they do, you can ignore them as then you're dealing with an idiot if you ask me). Of course situation #2 is euthanasia, and falls under strict rules (in countries that allow it) for a reason, but "evil"....
And I think that most people will agree that situation #1 is a perfectly justifyable reason to kill, still I've seen situations in which people were angry when the killers in such a situation were not acquitted due to the self-defense being the reason, and even brought an open mourning with symbolic empty chairs, so even that one can come into debate.
"Evil" always depends on where you stand, but in the end, actions themselves are not really evil, what counts is the intention behind that action, and how it is motivated. And after that no matter how you put it there's room for discussion.