This passage is about David consolidating his power. He is anointed kind of Judah. (P.S. Saul's son is merely installed king of Israel.) Then all of his enemies are killed, through no fault of David's, and while these deaths establish the conditions for him to be king of a United Kingdom of Israel, he takes no pleasure in learning of their deaths. Instead, he punishes all those responsible for them.
David is established as a noble leader. Maybe even chivalrous. I've mentioned several times how these wars remind me of medieval legends reporting in the Canterbury tales or Don Quixote. Obviously, the medieval legends borrow from these themes.
Civility is a tool of the oppressor. Is nobility? In the practice of law, there is a tension between zealously advocating for your client and behaving with professional dignity. I say dignity because things that fall into that category are often about status for the actor. I grant an extension because I am an upright lawyer, above the fray. Was that fair to my client who would have been advantaged by denying the extension?