If the DM is frequently contriving reasons for taking prisoners to bite the PCs in the bum then they'll be incentivized not to take prisoners. Good on you for not doing that.My goddaughter I just referenced was 13 when I taught her, by the way, and having enemies "defeated" and no longer an issue was fine.
Larry Hama, principle author of Marvel's GI Joe series throughout most of its run in the 80s and 90s, referred to the cartoon as morally bankrupt because of its lack of consequences resulting from all the fighting. I haven't given it much thought before, but just having an evil race you can stomp with impunity with no remorse might also be morally bankrupt.Media aimed at younger folks doesn't include graphic death very often. Back in the 80s, in G.I. Joe cartoons, Cobra soldiers always had parachutes when their aircraft got shot down, and with tons of laser blasts around, few people clearly got shot, much less died.