There's a lot about Doyle that Bodie doesn't understand. He doesn't understand that Doyle's guilt trips aren't the sign of a gentle heart somewhere beneath the hard-man exterior. He doesn't understand that when Doyle wounds someone with his sharp tongue, it's not usually an accident, and Doyle isn't unaware of the pain he causes.
He doesn't understand why Doyle dislikes killing so much.
Learning to kill someone without excuse or regret takes away part of a person's self. Call it part of their soul. That's why soldiers are told how evil their enemies are - an excuse, to satisfy that part of them.
Doyle lost that part of his soul out on the streets, before his cheekbone was shattered. Bodie still has that part of his - he doesn't understand that, either. Bodie will kill on command - but only if he trusts the judgement of the person ordering him to.
He doesn't understand that after killing someone, Doyle isn't guilty because of the wasted life, or the people who cared for the victim - he's guilty because he doesn't care about any of it.
And he doesn't understand that Doyle tries to avoid killing because he's scared that without that part of his soul, he'll learn to enjoy it. Too much.
-- THE END --