I don't completely agree with this as I believe there is nuance to the difference in how animals and humans are perceived in terms of innocence. As a cheap easy example, nobody feels bad for killing the Nazis in Wolfenstein 3D, but there was a bit of a hubbub about killing the dogs. While many would argue killing the dogs is certainly no more of a moral problem than killing the humans, we can ascribe intent on the humans as we know they are evil nazis who understand what they're doing. However, dogs are in a true and genuine way only a loyal animal could be, just following orders. You could imagine somebody might consider animals more innocent than human characters due to their inability to understand what is they're doing on a grand scale.
While what you're saying isn't wrong, i think it's reading the book from the back.
It's true that it's more accaptible to murder nazis in games than, let's say, innocent Children.
But the thing is that no one kills nazis in videogames because they are evil people.
People kill nazis in Videogames because they enjoy the power fantasy of killing people.
The People being nazis (or demons, or Zombies) is just a convenient framing so players won't have to think or feel bad about their desire for a murderous power Fantasy.
Now of course you're right that that is a difference in perception, but i have to disagree that one is more right or wrong than the other because the actual intent is always the same of a powerfantasy, using nazis is just trying to preempt feelings of doubt about the desire, because afterall "only a dead nazi is a good nazi" and thus you won't have to feel bad about that desire.
Sure. However, how often does it happen that devs specifically design, model and animate with great care sequences in which the player has to harm defenceless human beings? The GTA games, including the torture scene. The Call of Duty game with the airport scene. The Postal games. I cannot think of many more games. The rest of the violent games are about soldiers/people with guns fighting each other, not the player abusing a being without any capacity to retaliate, like an animal, a child, or a weaker human being in general.
I'm going to refer to the above, just replace nazis with "beings capable of retaliating".
It's not like enemies capable of retaliating ever have a realistic chance of fighting for their survival against the player.
The entire reason enemies in videogames generally have guns or other weaponry is to specifcy a power fantasy happening within combat scenarios inspired by real world Events, and to further challenge the player because a power fantasy feels all the stronger the more powerful the victim is.
But ultimately, the average videogame enemies capabilities to defend themselfs is also just a farce created to empower the player, no different than the monkeys in sea of thieves. They are a different kind of power fantasy, specifically to create a comedic tone in this case as i understand, but a powerfantasy of harming others all the same.