If I had seen LotR at or under 12, I wouldn't have slept for days (maybe with the light on) but I don't think I would have been disturbed by BP in the slightest.
If it's possible/fantasy or not, the images are still very brutal indeed. It doesn't matter much that the blood is black/green, it's the violence that's disturbing because the victims are quite clearly suffering.

*shrugs*