Mm, true, there are a lot of severe medical problems that cause no pain (at least not until it's far too late). Though it seems sensible to have pain to alert you to, say, bending your finger back too far, or touching fire -- that's an actual helpful warning that stops you from accidental injury. Then again, that sort of warning pain isn't conscious, I think it stops at the spinal cord or something.

Maybe I'll read a book about it when I'm not in a haze of drugs and ow.