I too have back issues (due to skoliosis) but for me it's more like a constant discomfort, can't imagine actually having to deal with constant pain... What you said about good and bad pain makes sense to a certain extent - but the reason for pain is just your body telling you something's wrong, it can't exactly tell you what to do - maybe we just haven't figured out what the right thing is?
Well pain is more of a "don't do this" than a "do this", but when it's broken, it's just "things are shit" which is like, "Ya body, I know, can you please stop nagging me about it since there is nothing I can do?"