I get no gratification based on the fact that the characters I'm killing in a game are men. If you're implying that men getting a sense of gratification from killing women in games is a cause for concern, as they might then feel desensitised about abuse against women in real life, I don't think that's a worry. I understand that some men might feel uncomfortable, depending on the scenario, for instance a torture scene.
But like @Brodehouse mentioned, nameless, cloned female npc's in a shooter shouldn't be any different. I'd like the opportunity to play a female soldier, it's something that I have noticed in past war games, while I know that the ratio of men to women in the army is vast, there are still strong women in the army and I think they should be represented.