|Decorus Goblin Squad Member|
Heinous Flag is not dependent on the mores of the owners of a hex.The owners of a hex can make illegal/legal whatever behavior they want... thru LAWS. Heinous is beyond that.
Slavery would continue to be a Heinous-triggering act regardless of if where you do it it is legal or not.
Remember, Heinous is 'Super Evil', and Good/Evil are not subjective cultural preferences in Pathfinder, but Cosmological Forces that one can't evade or alter. In PFO, Slavery and Undead-Creation ARE Evil and Heinous, whatever one thinks about them (i.e. even if they are 'perfectly acceptable behavior' legally and within the norms of a settlement, they still are Heinous, and that settlement itself will be strongly pushed towards Heinous because of it's sponsorship of Slavery).
The question remains whether there is any indicator/discriminator so that settlements can treat Slavery-Heinous differently from Necromancy-Heinous, or whether a settlement that wants Slavery-Heinous to be A-OK (people with this flag are still under protection of the law vs. being attacked unprovoked by others) must necessarily also treat Necromancy-Heinous the same, because there is no mechanical means to discriminate between those.
There are places in Golarion where both are not Heinous so when they introduce those areas into the game what then?
There are places in Golarion where being a Cleric, Paladin or follower of particular gods is considered Heinous what do you do when they are introduced into the game.
Followers of Asmodeus would not consider Slavery to be a Heinous act should they be able to get the benefits of murdering people who have the Heinous flag for being Slavers?
The Heinous flag is an extremely subjective thing at the current time its just the developers inflicting thier morality or more likely worry about being condemned by groups who would find the behavior offensive.