And this is a third question, about the nature of badness, for which pain is but a special case, not necessarily anywhere near the most salient one. I suspect pain only registers as an important example of badness because of availability bias, it's a particular incarnation of badness which people actually experience, as opposed to a concept of pure badness derived from an accurate theory of badness. You'd want to study the nature of badness, not the nature of pain.