There's a sci-fi novel I encountered years ago, and I've recently become fascinated by the premise, but I cannot for the life of me remember author or title.
The premise, as I recall, is this:
An Armada is heading from earth to another planet with the mission of destroying that planet. The reason for this mission is not an act of hostility by the planet's inhabitants, but rather because this (intelligent, I think) alien species requires a certain virus in order to reach maturity.
The problem is that this virus is deadly to humans, with a mortality rate of 100%, and presumably there were some serious problems with this virus at some point in the recent past.
The book (if I'm not mistaken) focuses on the actual voyage of the task force, with various characters becoming uncertain of the morality of what they are about to do. Hence, there is a great deal of moral debate in the narrative.
Does any of this sound familiar?