Ultimately, I get the idea that the option was "all life serves Zodiark forever as His thrall" vs. "mortal life has a chance to thrive on its own, create its own worlds, and live under its own rules." Ultimately, it depends on what you consider 'living' to be. I am currently operating under the assumption that the cost of living under a world where Zodiark ruled was too high, and therefore Hydaelyn's actions and creation were morally justified. A life where one is in perpetual servitude to a god that demands ever-increasing sacrifice and supplication isn't really 'living'. If Zodiark eventually had control over the whole lifecycle of the star, it's possible that the lifecycle could have eventually stagnated into darkness entirely, leaving just an endless expanse of chaos.

"In one fleeting moment from the land doth life flow
Yet in one fleeting moment for anew it doth grow
In the same fleeting moment thou must live, die, and know"