After thinking about it, I realized that there’s one character I probably would mistrust in the scenario in the OP:
Superman.
Now, true enough, there’s also enough variations in iterations of Superman throughout the various universes and continuities to make this problematic, even leaving out Elseworld Evil Supermen and whatnot, but hear me out.
Usually, when Superman is about to outright kill someone, it seems like it’s at a point in a story where he’s finally been pushed way too far, and isn’t thinking straight, and this is about the point where some other character jumps in and tries to talk him out of it. Usually with a “Clark, please listen to me, this isn’t you…” or a “No! If you kill him, you’ll be just like him!” Now I’m hardly a deontologist, so I’m skeptical—at best—of statements like the latter, but I’m at least willing to consider in that situation, Superman might be under stress and not making the best decisions, or that there might be other, more pragmatic reasons to try and stop him. (Like too many witnesses, or it’d give him PTSD, etc.)
(This is also leaving aside the possibility that he’s being mind controlled by a villain.)
But the other big thing—which to be fair also applies to a lot of other “never kill” superheroes, and not just Superman—is, well…Superman is a bigot.
At least towards artificial or exotic forms of life, like androids and AIs. He’ll kill and mangle them without hesitation, or a second thought. As I hinted above, I’m not one for keeping dangerous supervillains alive purely for the sake of morality, but thoughtlessly slaughtering them just because their “race” makes it okay leaves a foul taste in my mouth.
So if I see Superman about to kill an intelligent robot? I have to question if he’s doing it because the robot genuinely needs to die…or just because Superman has a cavalier definition of “person.”