For Jehovah's Witnesses: Why is it wrong to accept your own blood?

I'm not a JW, or even religeous at all, but I will say good on you for asking questions of your religeon. If something seems wrong or illogical, ask about it. If you are told off for asking questions, that person is probably scared you will find some information that conflicts with their indoctrination. Use google, and other resources to do your own research if no one answers your questions. Again, good on you for thinking for yourself, keep asking questions.