I'm going to chime in with a tangential anedocte from one of my campaign.

Some background: Pirate themed/investigative campaign, the party is a band of mercenaries aligned/helping out the local authorities of a maritime city (formermly a pirate stronghold, liberated centuries ago)

we're tasked with solving a kidnapping incident, noble lady X was taken hostage to a ship and they're sailing toward destination Y.

we give chase, along the (sailing) way we stumble upon a third party ship that's being assaulted by sahuagins, which are cannibals ( or whatever word you want to use for people eating sophonts ) and are generally regarded as monsters in-setting, despite having a rudimentary civilization.

Being a goodish party, we stop to help the beleguared vessel, at the cost of risking failing in our taken-upon duty.

The sahuagin party attacking that vessel is seemingly lead by a brutish "bigger sahuagin" raider with a beautiful female second in command, that looks like a normal sea elf.

The party leader, not knowing if it's a situation of coercion or whatever, uses nonlethal force to take down the sea witch, every other enemy combatant was attacked with lethal force.

In the post battle interrogation/fact checking, appropriate knowledge checks let us known that the beautiful sea witch is a rare subspecie of sahuagin, she may look like a beautiful sea elf, but she is a sahuagin, with sahuagin values and behaviors.


At that point, I find myself arguing against the party : the rest of the party (mainly the party leader, the other players are passive when it comes to making decisions) wants to let the sea witch go, if she promises to stop "her wicked ways" of raiding ships for plunder and eating the deads.
I argue we should kill her right then and now: if we let her go she'll simply go back to do as she did before and I would feel guilty in my coscience/ responsible that any further harm she'd do from now onward would indirectly be my/our fault.

(aside: I in character brought up the classic "what do you think would happen if adventurers tasked with exterminating a nearby raiding goblin enclave comes back to the village with goblin pups/childrens?")

In the end, the party leader took it upon himself to bring the sea witch with us back to the city for "re-education", I told him straight that if that resulted in some kind of tragedy, I would consider him responsible for said tragedy.
(aside: that character of mine feels "neutral/what's the big deal" about cannibalism, because being a draconic saurian himself, his general philosophy on the matter is "a person stops being a person when they die, meat is meat" corroborated by the generic dragon-related clichè of "dragon blood is strengthened when asserting superiority over other dragon stuff, especially if you consume the weaker party")

It was a very interesting character development moment, because during that discussion it came out that the whorehouse my character was associated with (character archetype was a courtesan/bard/high court retainer) employs one succubus among the staff, which I (the player) knew about, but I ( the character) didn't, and I was kind of dogmatic in the "Evil outsiders are abominations that should be killed on sight", but she was just trying to make a living while enjoying doign her life drain, but taking precautions to avoid "draining to death"

Anyway: from then onward my character teased the party leader that their(the party leader) qualifiers for "evil/monster" not deserving of mercy and "not evil/person" deserving of mercy is a pretty smile and a pair of tits