Evil effects often manipulate energy from evil-aligned Outer Planes and are antithetical to good divine servants or divine servants of good deities. A creature with this trait is evil in alignment. An ability with this trait can be selected or used only by evil creatures.
Buried in the back of the book is an absolute prohibition on non-evil characters using anything with the evil trait. Both the Demonic and Diabolic bloodlines give abilities with the evil trait, however.
Diabolic's second and third bloodline spells (Embrace the Pit, Hellfire Plume) are both evil, making the feats to take them null (Unless for some reason you want more castings of Diabolic Edict).
Demonic gives the 5th level spell Abyssal Plague, which is also evil. And unlike Diabolic you are forced to take this as part of your spell repertoire, but can't ever cast it.
Should I just avoid these bloodlines for now for PFS2 characters?
|⦵⦵ Sebastian Hirsch Venture-Captain, Germany—Bavaria|
Yeah, having issues with both those bloodlines myself. Really liked the flavor of the infernal bloodline from PF1, but giving both demonic and diabolic bloodlines the divine list is just thmatically wrong IMO. Really hope Paizo rethinks this or at least comes out with an archtype to allow those bloodlines access to arcane spell list.
Interestingly, in one of the social media interviews somewhere, the question of evil descriptor spells came up, and the impression given by devs was 'not a big deal individually, it's how you use the spell that matters more' - and I even think this was brought up in relation to organized play. Which is not what this line in the book is saying, assuming (as we should on the face of it) that spells are categorized as abilities. (It may be future proofing for feats that have the tag, and someone missed that spells would also be affected here, but it will definitely need calling out soonish.)