If a person wants to decline treatment even knowing he will die, I've got no problem with that whether that choice was based on some religious belief, superstition, or potential quality of life. But why people blindly follow irrational religious rules without some serious study is beyond me.
Reminds me of the story of the woman who made pot roast and always cut the end off before cooking. When asked about it, she always said it's how her mother taught her, and her mother made wonderful pot roast. On one occasion, her mother was visiting and her husband, having been curious all this time, asked why she had done that. The mother said "because I never had a pot big enough for the whole roast." Often asking "why" is a good thing.