[My question is based on the relationship depicted in the films.]
Recently, I watched all the X-Men films again. I understand that Wolverine is supposed to be an angry dude. But I was surprised by just how many people he kills onscreen. More than any other character, for sure. And in many situations, it seems superfluous, for instance,
In Days of Future Past, in his first scene after he gets sent back through time, he gets out of bed and immediately kills three people.
I say "superfluous" because in many situations, incapacitating the enemy would suffice, and of course, Wolverine is almost never personally in danger during any of these encounters, because he's essentially indestructible.
Moreover, Wolverine doesn't just kill "bad guys," he also kills —
Fellow mutants. For instance, The Last Stand, he kills a lot of them during the final battle on Alcatraz.
I grant you, Hugh Jackman makes the character completely appealing. But if you objectively assess Wolverine's actions during the films, he's at best a loose cannon, and at worst a mass murderer, because many of the killings lack reasonable justification.
But the question is about Professor Xavier. We can understand why Prof X would see Wolverine as useful, or be sympathetic to his trauma, e.g. —
His manipulation by Col. Stryker.
But given that Prof X is a man of peace and tolerance, why is he often shown expressing warm feelings toward Wolverine?
Like in the last scene of Days of Future Past. We also learn that he has given Wolverine a teaching position at the school. (Angry dude + kids = is that really a good idea?)
For that matter, why does he associate with Wolverine at all? He could ask any mutant in the world for help — why does he habitually rely on a guy who is categorically violent?
(And if Prof X knows that Wolverine kills repeatedly on his behalf — as he must, not least because of his psychic powers — what does that say about the strength of Prof X's convictions?)
Is there specific evidence in the films, or other places in the Marvel universe, that would explain their seemingly incongruous bond? Since Wolverine & Prof X are friends in the comic books as well, it's possible that the movies have depicted a small aspect of their relationship without filling in the nuance that would make it consistent with the characters.