Question about merpeople

[Thomas Jones]

I know it has been implied in their write up for the bestiary and elsewhere that the whole race has some sort of dark secret. Have we been given any idea what that secret might be?

[Snorter]

They save resources on prisons, by selling their undesirable citizens to local fishermen, in return for forged metal items.

[Jeven]

They were depicted as a sinister race in the short story in the Legacy of Fire AP.
The impression I got is that their hostility to seafarers stems from human abuse of the race, and they return that with cruel, deadly tricks such as sinking ships and luring sailors to their doom.
They don't seem to be evil but rather enemies of humans because of generations of conflict. So its something akin to a blood feud.

[Wrong John Silver]

Well, considering the history of gillmen and Azlant and the aboleths, there are plenty of possibilities.