Originally Posted by
Tavrobel
The simplest answer to the question of WHY to summon Dream Zanarkand, is to preserve the integrity of the city; even if they could no longer do so with actual substance. Most of the Zanarkand citizens felt that they were wrongfully attacked by the people/machina of Bevelle, and most of them slaughtered. Fearing the destruction of themselves, they offered themselves to Yevon (who was at that time, gathering recruits to rebuild this marvelous project).
Yevon however, exploited them (in a somewhat friendly sense; Yevon likely knew many of these people as its leader) to use their power as a weapon. Sin is a direct cause of the citizens; without them, there is neither a dream, nor Sin. He felt that this was the best way to both protect his people, AND defeat Bevelle, instituting his tyrranical rule.
While Sin was not necessarily desired by the people, it did win the war for them, despite the heavy cost, and protects DZ from potential threat, by nipping technology in the bud, and keeping people in constant fear of Yevon, which was his plan in the first place. The citizens of Zanarkand WANTED TO WIN (well, technically all they wanted was not to lose). Sin made them win. They are NOT the enemies of Sin, nor its summoner, Yu Yevon. However, after 1000 years, would you not tire as well? The Fayth may have the power, but they do not have the will to act, nor can they be guaranteed of dealing actual damage.