I think the reason I find this unnerving, is that terrible events unfold, and it is not happening to them because they are bad people. Inexplicable chaos exists, there is nothing guiding it. It feels like being plunged into darkness, just because and trying to find a way out of it.
I think the film also works as a defamiliarization of the treatment of cattle, by changing cattle for humans. To see the horror of it. There are also some really powerful shots in this, that burn themselves into your mind. A horror classic.