The Stars are Alive
The Sun god is always the good guy who turns undead and is lawful, demons are far-away stars (based on LotFP's contact outer planes bit).
Since each star is a sun in its own right consider the following:
Stars are lawful to those evolving on their planets, nurturing them to pick up science and civilization and shun magic and disruptive sorcery. Other stars meddle by granting power and sowing chaos, trying to get the local populace to abandon civilization and devolve to magic use.
Adventure Seeds/Gameable bits?..
Option A.) Each star hinders or helps civilization through religion to try and guide its populace towards advanced robotics prior to interstellar travel so the star can just shed off these corruptible biological entities and build itself a mobile Dyson sphere and eat the fuel of other stars.
Option B.) Each star is looking to turn its people into a star faring civilization to act as conduits to begin psychically enslaving other stars.
Not sure which option I like more. Leaving one as the story being told to the clerics and one as the story told by other stars is a good option as well, create doubt.
Other notable contributions:
"As technology advances, light pollution is nurtured by Sun Gods because it keeps other stars' light from human perception, reducing their ability to influence local humans."
"Planets are opaque prisons locking subdued radiances in a solid core, the end result of capturing another god in a contracting dyson sphere and crushing it down to a tame, manageable size. Best way to jumpstart a new cult to eventually drag you off to the next victim.
Planetary cults (the Old Gods of the Earth) hearken back to this older divinity, but don't really have a future worth mentioning."
"So undead, because they rely on nonsolar sources of energy for their biological processes, are inimical to everybody?"
My Response "I just pictured undead as abominations that other stars showed each others populations to summon to help meddle and overthrow civilizations. Every star knows how to make undead (and thus turn them), but they only show the populations of their neighbours stars how to make them in a bit of sowed chaos."