Yes, I also felt the patients (and victims) were as passive as any of Conrad's Africans in "Heart of Darkness." This is necessary for the protagonist's con, of course, though it seemed a little odd that their rituals would come back to "get" the white, Christian witch-doctor (a neat reversal here) when they didn't seem to have much of a presence earlier. I don't know if that's the writer's fault, seeing as how the DENTISTO doesn't speak Spanish and has never bothered to learn, so there's no way the Mayans would be communicating with him.
Overall, though, I enjoyed the horror that played out here. It felt real, visceral, and shocking. I believed - by the end - that this self-serving prick has many cousins in the Third World operating their rusty saws as I sit here typing on this forum...
The way you walked was thorny, through no fault of your own. But as the rain enters the soil, the river enters the sea...