The Federation Council debated whether or not to give the Dominion the cure to the morphogenic virus, but decided against it as they felt it would give the Dominion "the upper hand" in the war.
It'd be like the Allies finding out that all of the senior Nazi leadership has AIDS or syphilis, and, despite having developed a cure, decided not to hand it over.
"Captain, we are being hailed. That is, if you don't mind...if it isn't too intrusive."
Loyal member of the Militant Janeway True Path Devotees