The reason the ending is the way it is (spoilers)

I understand how people were frustrated by the demon surviving in the end, but I think there's a good reason.

I think there's a symbolic metaphor that the director wanted to communicate. Although we're watching a specific narrative based on an absurd parallel universe where demons pass by touch... I think it was meant to make us think about when people in real life do horrible things that are difficult to explain.

It's like they would be possessed by a demon in that terrible moment. And the nature of evil energy passing body to body is related to how the way we treat others can stay inside the mind, while they carry it to other experiences with other people, where the demon can come out.

Comfort the disturbed and disturb the comfortable