I didn’t see the film but it sounds like there is famine and sickness running rampant, out of control. The human sacrifice restores morale because it unites the people and rallies them around their identity as a people of destiny, as special. It stirs up in them the belief that they will not be vanquished by the famine and sickness which fill them with fear. I think the community succeeds in excluding the voice of the victim by its frenzied unity and because they are pouring all of their fear into the ritual as a release valve. When a whole community is caught up in fear of perishing then the desire to be freed from this fear becomes utterly compelling.