Morally interesting plot ideas

…and Depeche Mode (because I’m listening to my 1980s station on Pandora).

Get the Balance Right
Premise: The PCs set out against a foe only to find out that their foe is holding another potential foe at bay.
The Problem: If the PCs defeat their enemy, they run the risk of setting loose another danger.
Explanation: Two dangers are locked in a struggle of some sort – each of them is expending their resources on this struggle… and each is being weakened by it. Moreover, their attention is largely focused upon each other. If the PCs intervene, they will likely upset the balance of power between the two. One will emerge triumphant and – without the other as a distraction- will turn its attention to the rest of the world. Will the PCs upset the balance of power or will they restrain themselves and act to maintain this balance even if it means helping their enemy?
Example: I was playing in a Greyhawk campaign once, and we needed to rescue some prisoners from the Scarlet Brotherhood, a nation of devil-worshippers. It turned out that we had the opportunity to strike a major blow against them. Of course, the Scarlet Brotherhood served as a buffer argainst the domain of Iuz, a demon-godling. Did we weaken the Scarlet Brotherhood enough for Iuz to destroy it and begin focusing upon others?

People Are People
Premise: The PCs are set against a foe who ends up not being their foe…
The Problem: The PCs have an ally who has an enemy, but that enemy isn’t evil except from their ally’s point of view.
Explanation: The PCs are told about an enemy from an ally (or, perhaps, someone they are courting as an ally). Their ally doesn’t lie about its enemy and presents it as evil. When the PCs meet the enemy, it may appear threatening if they don’t look too closely – but, really, it is far from evil (though definitely dangerous to their ally).
Example: In an Exalted game I ran, the PCs sought help from a powerful forest spirit. This spirit was living in terror due to the fact that horrible monsters were slowly killing it. The PCs tracked these monsters down and found giant beaver-men (who were clearing the forest).

Master and Servant
Premise: An evil ruler’s subjects do not want him to be overthrown.
The Problem: If the PCs overthrow the evil ruler, his subjects will be unhappy – and potentially far worse off than they were.
Explanation: This one could go a number of different directions. Perhaps the ruler is good to his own subjects, but conquers, tortures, and enslaves others. Perhaps the ruler is only tolerable because he maintains a strong army that protects his subjects from neighboring dangers. Perhaps the ruler has enslaved the minds of his people – whether through brainwashing/propaganda or actual mind control.
Example: Ummm… I can’t come up with a good example of this one from my own gaming history off of the top of my head, but I think the problem is clear enough.