I agree, Fasold, and that’s also part of why I’m a roleplayer, nevertheless, my answer will be twofold:

1. okay, hack & slash killing can be “entertaining”, to a point, as a stress reliever for the evening if you will, like you just said… I support that. And I add such fights in my games because of that. 🙂
2. nevertheless, I insist that it’s not about killing, it’s about shooting stuff or just about the stress or the intensity of it (à la Hitchcock). In my games, the fighting happens as it should, that is: if you kill 10 people, there’s going to be blood & guts everywhere, you’re gonna stink like a slaughterhouse (which is exactly where you’re standing by the way…), and people around you are going to react to the smell and to your actions.

So now no matter who or what you’ve killed, even if it was just game (animals that is), the basic idea is that like sex, killing (most types of it anyway) is dirty, so it shouldn’t be the only fun there is. Adventuring, or spying or solving puzzle or stuff like that should be more fun than killing. Killing should be just an accidental event (to relieve the tension if you will, that’s how I’m using it. 🙂 )