(begin mild rant)
A common misconception about Alignment: That it's simplistic. It's not. It's anything but...
Just because the DM can put a label on your actions and declare them Good or Evil does not affect why the PC's are struggling and what they're doing in the slightest.
Just because something's Evil doesn't mean it's OK to kill it...it's still a human being with complex thoughts and feelings. There is a reason it's evil, and there is still a motive behind it.
I happily include alignments in my game (in Planescape, it'd be hard not to). Alignments simply define what is. They don't give you a preprogrammed excuse to do things.
IMNSHO, any DM who allows Alignments to be used as a shortcut for moral consideration is being lazy. There's also the greater problem with the characters detecting and knowing alignment. IMC, PC's don't decide their alignment, I do, based on how they act and what they tell me.
It's simply a tool to define what cosmic force is powering a creature at the time. Not something you need to unceasingly obey or something that is to become a justification for killing. It's not a straightjacket, either -- only the exemplars of the alignments are said be nearly 100% examples of their alignment all the time. Paladins can break the law, evil people can raise a loving family, barbarians can adapt to the obviously lawful pattern of speach...and that's not cause for alignment change unless they do so consistantly, and prove that this is their stance on life.
And it's also one of the easiest things to remove from the game if you decide you don't want an energy of Good like there is an energy of Electricity.
I think that terrorists who attack my country and kill children in the process are evil. On the other hand my military was torturing children in quantanimo bay. So if this same military that fights evil at one time and propogates it at another evil, good, neutral or is it dependent on the situtaion?
To keep the thread alive, I'll assume that this 'reality' is in a D&D game and not in real life. That people are attacking some nation, and the nation in question is torturing children.
In a D&D alignment spectrum, both would probably be classified as Evil. Simply fighting evil doesn't make you Good...evil more often fights itself because of it's inherently selfish and painful nature.
Without the D&D alignment spectrum, this is just a bunch of stuff that happens...one side attacks the other, the other side attacks back, big deal. They could summon an army of fiends or celestials to their side and not be good or evil about it.
So stop griping about it, people! There's no real reason to not like it from where I'm standing, and I'M a relativist IRL myself! But the philosophical defence of relativism has always been that there are some extremes that you'd be hard pressed to label as good, from a purely biological and evolutionary standpoint. In some regions of Africa, ritually mutilating the genitals of the woman is common practice, and is considered Good. Would you say that mutilation is a Holy thing? That if they think it's Good, it is? How about the Holocaust? The ones percipitating it certainly thought it was Good and Pure and Right! (Actually, DO NOT Answer these here, as it probably will cross the line and get the thread shut).
I want a fantasy world in which the PC's fear falling into the clutches of a demon because the moment the arbitrating force of the multiverse sees them as Evil, they'll be reborn in the Abyss. If I run a game without alignment, a lot of the dramatic tension is removed, and the PC's deal with devils as it they're orcs and bugbears, but with magical powers.
(end rant)
Look, I personally believe that absolute Good and absolute Evil aren't as absolute as all that...but that has exactly 0 bearing on me running a fantasy game in a universe that DOES have that, and just because I do run a game like that doesn't mean that it's simplistic or a shortcut or has no moral tension, any more than if there were an absolute Good and Evil IRL eradicating complexities, lengthy discussions, and moral tension. These things can still exist in an absolute universe. Alignment doesn't prohibit or even make difficult any of these, and I've found that it actually enhances the fear when the PC's know that being evil will actually make them Evil, when there's a tangible effect to be placed on the PC that they don't like.