When David beheaded Goliath, he violated rule 113 of customary international humanitarian law which prohibits the mutilation of corpses in war. Interestingly, that was never addressed when I learned the story in Sunday school.
I know what you’re thinking: “That’s anachronistic! You can’t judge an earlier action by a later law!” But I’m less interested in the law, per se, than in the objective moral standard that I believe it correctly tracks. I think it is objectively wrong to mutilate corpses.
Doing so is a desecration of the human person, a violation of the image of God, objectification to make it easier to kill. Interestingly, when it comes to biblical violence, many conservative Christians end up sounding like cultural relativists.
Hey, by the way, next Monday I am debating Paul Copan on biblical violence for Unbelievable with Justin Brierley. The show should be out in later October.

