In the course of daily life, the forms and the substance of a bourgeois democratic polity are important. You cannot properly claim to be a genuine democracy if the people cannot claim to exercise the soverignty. In a sense, warfare is the final claim constitutive of sovereignty. Therefore, if the people cannot be said to determine whether Section 31 wages war against the Dominion, the Federation is not a true democracy, whatever characters may say on screen.
The defense of Section 31 hinges on the unsupported, even mostly unacknowledged, "principle" that the world is in fact a constant warfare. Thus, Section 31, like all covert operations branches, must fulfill the needs of this ordained necessity, and notions about democratic control are merely whimpers for a vain illusion.
But, in either case, whether the government is formally certified by the customary forms as representing and executing the will of the people, or whether responsible parties perform their (tragic?) duties, the legitimacy rests upon the assumption that warfare is the natural order.
I say again that is merely reactionary ideology. Warfare is not an inevitability. Indeed, in scientific terms, interstellar empire and warfare are ludicrous. It is merely assumed so as the politically correct thing to believe in a backward society. All aggressive warfare is wrong, as a crime against peace, from which an ocean of evils stem.The show wrote the Dominion as insanely aggressive merely to allow the Federation to be portrayed as fighting a defensive war. However..
Since the Dominion could only attack through the wormhole, it was merely necessary for the Federation to deny them control of the wormhole and any Dominion invasion force would be doomed to failure.
Even given the on screen circumstances as portrayed, the genocide was unnecessary, save as a desire to daydream about how "we" need to respond to our current enemies.