Perception can dress up the ugliest of ugly and this applies directly to this question. They were "uncommon criminals" and there actions were the actions of evil people. At the nature of each of there killings was an evil action, killing people is evil.
The same questions could be asked of Robin Hood to some he is a hero, to others a common thief because depending on where we look at the situation from our viewpoints on the thievery of Robin Hood can be seen as good or evil but at their base nature they were criminal actions. Theft is the action of a evil person. So while the added context of "good motives" in the case of Connor MacManus and Murphy MacManus in killing evil people and avoiding women and children while doing their killings of the perceived as evil people of the world is allowing us to see the actions of these "Boondock Saints" as good.. the fact of the actions nature has not changed.
Killing people is evil. This question has the qualifier of "ultimately" and by that I infer you mean "at its base" or "at its nature" so in this answer I have described how each of these fictional characters, Connor MacManus, Murphy MacManus and Robin Hood, have committed "ultimately" evil deeds and the layers of context and perception need to be peeled back and removed to see something "ultimately" or "at its nature". The nature of all of these crimes is evil.
I want to see the MacManus brothers and Robin Hood as good people and it is not hard to do so but then I am not looking at them "ultimately" I am looking at them and their actions in a context that allows this good perspective. Without the context of the story behind the actions it is impossible to see thievery and murder and "good" so in the above mentioned cases the evil actions of the protagonists are merely dressed up as good actions in the context of "good motives" and "for the right reason" while each of their actions was at its base evil.
Evil. Although that word doesn't sound right. The end NEVER justifies the means.
I realize its easy to think that all these kind of gangsters should be killed. And they should, but it should be done after a trial. All men good or evil are entitled to a fair trial.So going vigilante and killing these guys is wrong.
P.S. The second movie was terrible.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.