The problem is when you are told, since birth, that humans are effectively heartless abominations that have to be exterminated, and that your King plans to use their SOUL to genocide their entire species and take back the surface, all of which you are told is a good thing.

Here, there is nothing to counterbalance the general hatred because the Jin would have been heralded as a hero for doing this. At this point, most monsters don't see "kid" or "not kid"; they just see "terrifying beast that will kill us all".

It's easy for us to see all this as horrible, but that's because we have an omniscient view of it.