Back in the day, quite a long time ago, I was playing the original Fable: The Lost Chapters game. Unlike most other RPG-like games, it has side quests that can be considered "good" and others that can be considered "evil" (and which affect your morality stats in the game). A good quest is for example helping someone, while an evil quest involves for example stealing something or, in the absolute worst cases, massacring an entire village of innocent people who have done nothing wrong.
One of the problems with the design of the game is that the quest list didn't really make it crystal-clear which side quests are of the "good" kind and which are of the "evil" kind. So at one point I accidentally accepted an evil side quest without realizing that it was such. And it wasn't just an innocent "steal candy from a baby" type of evil, but literally a "massacre an entire village of innocent people" mission.
Well, no big deal, just cancel the quest? Turns out that once you have accepted a quest you can never get rid of it. At least in the original game there literally is no way of getting rid of a quest that you have accepted. Nothing. The only way is to load a save that you had made before accepting the quest. The problem? I had since long overwritten that save, and didn't have one. The only way around this would have been to start a completely new game.
Well, what's the problem? Just ignore the quest and never do it.
Problem was: The village in question connected two areas of the game, and there was no way around it in order to get to the other area, and traversing between the two areas was mandatory to advance in the game. And the kicker? Once you entered the village in question, the quest would start, and there's no way of just ignoring it. You literally cannot leave the village without completing the quest! The game just tells you that you can't leave because you have an unfinished quest there! You are stuck! The only way to get "unstuck" is to load a save from before you entered the village, but that just puts you back there.
Yes, the game was literally designed (I don't know if deliberately or just because of lack of thought) so that if you had accepted a quest that involved doing something in such a village, you literally could not traverse through the village without doing the quest. The "optional" side quest becomes a mandatory quest, if you want to advance in the game.
And to put even more salt to the wounds, if you actually started killing people in the village, they would cry and ask you in desperation why you are doing that.
This game design was completely asinine: If you accidentally accepted a particular side quest that was this morally evil and bankrupt, it had the side effect of indirectly becoming a mandatory quest because you couldn't bypass it and thus you couldn't advance in the game without completing it, and there literally is no way to cancel or ignore the quest, once accepted. And to punish you even more, you have to witness the suffering of the innocent NPCs in order to complete the quest, and there's no way around it. And the thing is that the quest descriptions don't always make it clear if it's this kind of evil quest or not.
But this has got me thinking many times: Why do I have a problem in killing certain fictitious non-playable characters that are nothing but pixels on a screen (and thus they don't exist as real sentient feeling beings), while I have zero qualms about killing certain other non-playable characters (in some games even quite brutally so)?
From an ethical point of view, at least one line can be drawn: If the NPCs are trying to kill me, then it becomes morally justifiable to engage in self-defense. Likewise if the NPCs are threatening other innocent NPCs it's morally justifiable to stop them from doing so.
However, that's not all possible situations that can happen in such games. Sometimes, for example, you may approach an "enemy" NPC from behind, without him noticing, and killing him by shooting or stabbing him in the back, without even knowing if he was going to attack you or not.
Most games make it relatively clear whether such an NPC would attack you for sure if he sees you by, for example, establishing that NPCs wearing certain unforms or certain clothes will always automatically attack you, without exception. Likewise a common game design is that all NPCs within a certain clearly delimited area will always attack you without exceptions (while NPCs outside of that area will not). Thus, it makes it morally easier to kill them before they see you, because you know that they would attack you anyway, so you don't have to actually test and make sure that's actually the case.
In a few games it may be less established. Sometimes it may be harder to distinguish between NPCs that are "enemies" and will automatically attack you, and those who are not. In fact, when this is sometimes the case in some rare games, I myself usually do hesitate before going into a killing spree and usually prefer to wait to see if the NPC will attack me before I respond in kind.
But it's an interesting psychological question what makes many/most people behave like this. These people know perfectly well that these are just some pixels lighting up on a screen, depicting completely fictitious non-existing non-sentient non-feeling imaginary beings, and it makes literally no difference to anything whether you simulate "killing" them or not. Yet these people, including me, still hesitate killing "innocent" people, even if they are completely fictitious and simulated.
I think that there's more to this than just weird psychology in play. Regardless of whether these people are fictitious or not, it can erode one's principles, morality and sense of psychological well-being to act in a manner that goes contrary to one's moral and ethical values. It can feel bad, even knowing that no real being was hurt in doing so. In fact, it's not true that no real being was hurt: There was one real being who was slightly hurt by these evil acts: You yourself. Doing bad things to innocent people can feel bad, and that hurts. It obviously doesn't hurt even nearly as much as if you were to do it to a real person, but a hurt is a hurt nevertheless, big or small.
Maintaining your moral principles even in a completely simulated fictitious setting can also work as a safeguard against you losing or eroding those moral principles. Who knows what will happen to your moral principles in real life, if you slip up on them in these video games? Will you become more and more desensitized to evil acts over time, slowly but surely, if you just keep doing these simulated evil acts yourself? It's not completely impossible. Even if simulated, doing evil acts can have negative psychological consequences, like so many other things may.
