With the offering of rebellion presented I shouldn't be surprised everyone seems ready to jump ship for a mysterious ancient vampire. A vampire, who we should compare to Victoire for a moment:

[indent]Will not trust her subordinates to have the free will to act against her intentions and ensure mechanism to control them.

Shall consider you a food source until proven otherwise.

And will find new and inspired ways to violate you that even Fran would find too demeaning.

Is blatantly aligned with cosmic horrors outside the Nexus seeking the ruin of everything done since anyone stepped foot in the Nexus[/indent]

So to speak on behalf of the Three Factions defense and, indeed, the eternal conflict in general, here's a few pros to balance out the cons:

[indent]One, fighting is your job. Professional Soldiers, to put a label on it, and like every job it exists to sustain you. Is it really a horrible thing to ask the people who have wildly destructive powers which excel in inflicting harm on others to then use those powers on other factions, in exchange for whatever it is they need to enjoy their immortal lives? Henry and Victoire live in castles, the Angels have a captial  city were even the slums could be made of polished marble and gold, and the Machina can fabricate basically anything you can think of. Not to mention the spoils of war you take home after the battle...

Second, let's say peace is achieved, then  what? Danmaku duels and inter faction orgies settle everything as they prance through fields of wild flowers and bunnies? Let us not forget that the factions and its people, in general, are opposed to their enemies in ways of  ideology, temperament, and culture. That they share commonality in their arrogance and avarice isn't going to do much to bind them together. Even though individuals may get along, as neighboring nations they would have a great deal of enmity towards one another even if they weren't actively fighting.

Third, would the PCs really be able to live in peace? Over countless years of conflict they have all the moral restraint of Charles Manson and while I doubt Omega or the Maid Twins would have trouble living on the straight and narrow, expecting the Demons to stop raping and pillaging is a bit much. And when you have high and mighty angels proclaiming their greatness from the heavens, mankind is  going to get a bit miffed when a Laguna steps on a city and treats it will all the severity of trodding on ants.
[/indent]

Its like watching a star think its getting dizzy and halting its own rotation. The catastrophic end result is only on the one halting the momentum. 

But that's me speaking for the Faction Leaders. Do what you must.