Given some of the explanation from the story
Hydaelyn nor the Ascians want Voids of Darkness OR Light. Elidibus atleast doesn't want it because Zodiark apparently doesn't want it as such, though it still seems malicious anyways. If anything depending on how the whole thing with Hydaelyn and Zodiark went down (because we almost certainly have a lot more to learn about that conflict), Hydaelyn might even be okay with Zodiark not being sealed since that would probably help keep the new balance...though of course he might just try to take all the shards/realities into himself instead so who knows. Regardless Hydaelyn still seems to be in favor of life.
It does, though, give some justification for being a Dark Knight.