Me at page 8: "Uh oh is Yajin about to merc some children?"
Me at page 22: "Sorry kid, your childhood ptsd is about to start."
It's an interesting question. Humans form social bonds and moral codes within their own communities, but those moral codes wouldn't apply to outsiders. Anthropologists who study pre-agricultural bands of hunter-gatherers note that when a member of the tribe tries to steal or rape too much within the tribe, they usually end up murdered. But the tribe is very willing to murder/steal/rape a neighboring tribe. The mechanic of "In-group vs. out-group" is common throughout the world. The new guy in town is a mark because they're outnumbered. Similarly the community will elect strongmen to protect their group from outsiders.
It explains why the town would be ok with a fratricidal monster as the head-fisherman and willing to murder and rob a traveller.