We disagree, probably because I don't believe it's a sin and I suspect you do.
Cannibalism seems to have been forbidden in the Mosaic Law of the Old Testament. I suppose it could be found elsewhere in the Bible. I don't know.
But something about it is repellent to me more than the thought of dying.
I also think perhaps Catholics have an easier time of accepting it, considering their view of the Lord's Supper. I know Shanley, who adapted the film from the book, was raised Catholic.
Sometimes pragmatism isn't always the highest goal.