I can certainly see your point. I guess it comes back to whether good or evil can exist without choice. The main reason I brought up Dungeon Keeper was because it often pits you against other narratively evil foes, as well as good, and I was arguing that evil fighting evil doesn't necessarily lessen the evil of either side.
There's always choice, even if the game you're playing doesn't present one. I chose to quit playing Dishonored relatively early, because I couldn't see any effective way to not kill everyone that was hostile to me, or more importantly, to not cause massive amounts of deaths due to the plague as a result of killing all those people. I'm not too troubled about killing people who attack me in a video game, especially after I've been framed for something, but in Dishonored doing so just screws over everyone else, all the citizens, and you're doing it all just to potentially rescue a couple people, if they're even still alive when you get there. Why is that worth it?
By comparison, in Skyrim, when the guards in Markarth decided to frame me and came to get me (and killed Lydia in the ambush outside the temple by hitting her with a spell aimed at me while she was kneeling), I didn't even consider surrender. I just killed them until I started to wonder if they were respawning, somehow, and then I left and killed all the Markarth guards I met on my way out of the province for good measure.
On the other hand, at the end of VtM:B, someone tried to attack me who couldn't really do me any real harm, and I just walked past them, ignoring them completely. If they can't hurt me, and aren't going to hurt anyone else I care about, I have no reason to retaliate.