"When is pain worst?" an is important and deeply related question which is, fortunately for us, much easier to examine directly. I feel worse to have a papercut than it is to have an equally painful, but ultimately more damaging cut elsewhere. I feel worse to have a chronic pain that will not go away than I do when I feel a brief pain that goes away shortly after. I feel worse if I am unable to fix the injury that is causing me pain. It feels unfair, awful and even unbearable to ache for days during a bad bout of the flu. I know that the pain doesn't serve me any useful purpose, it isn't going to make me any less likely to catch the flu, which makes it all the worse. Likewise, if I've hurt my foot and it keeps on hurting even as I walk over to the cabinet to get out a bandage and some disinfectant, that is worse than a pain that hurts just as bad for a second and then stops once I've stopped doing the thing that injured me.
This seems to indicate that pain is worst when there is a conflict between my objective assessment of my injuries and what my "gut" tells me about my injuries through the proxy of pain. There was a post somewhere on this site, perhaps by Yvain and I'd thank anyone that could find it and link it, about how there is not a single unitary self, but rather many seperate selves. I suspect that the main reason why pain is bad is due to a conflict between these many parts of me. Pain is at its worst when "rational, far-mode assessor of injury" me is at odds with "hindbrain, near-mode tabulator of pain nerves" me and the former has no way to get the near-mode brain to stop sending pain signals even after my initial panic at being injured has been overridden and all useful steps towards recovery and preventing future injuries have been taken, while the latter can't keep the far-mode brain from constantly ignoring these dire warnings about how my nerves are reporting bad things and how my skin is cut and how I'm probably bleeding and how it hasn't stopped and I need to lie still and wait to heal. The two argue in circles somewhere in the back of my mind leaving me with a certain unease that I can't but at rest by either laying still and resting or by ignoring my pain and going on with my day.
That is why pain is bad. Because, on some level or another, it causes different parts of me to come into conflict, neither being able to overcome the other (and neither should, for I shudder to think of what would happen if one did win out) and neither being able to let me rest.
Some time ago, I came across the All Souls College philosophy fellowship exam. It's interesting reading throughout, but one question in particular brought me up short when I read it.
What, if anything, is bad about pain?
The fact that I couldn't answer this immediately was fairly disturbing. Approaching it from the opposite angle was much simpler. It is in fact trivially easy to say what is good about pain. To do so, all you need to do is look at the people who are born without the ability to feel it: CIPA patients. You wouldn't want your kid saddled with this condition, unless for some reason you'd find it welcome for the child to die (painlessly) before the age of three, and if that fate were escaped, to spend a lifetime massively inconvenienced, disabled, and endangered by undetected and untreated injuries and illnesses great and small.
But... what, if anything, is bad about pain?
I don't enjoy it, to be sure, but I also don't enjoy soda or warm weather or chess or the sound of vacuum cleaners, and it seems that it would be a different thing entirely to claim that these things are bad. Most people don't enjoy pain, but most people also don't enjoy lutefisk or rock climbing or musical theater or having sex with a member of the same sex, and it seems like a different claim to hold that lutefisk and rock climbing and musical theater and gay sex are bad. And it's just not the case that all people don't enjoy pain, so that's an immediate dead end.
So... what, if anything, is bad about pain?
Let's go back to the CIPA patients. I suggested that they indicate what's good about pain by showing us what happens to people without any: failure to detect and respond to injury and illness leads to exacerbation of their effects, up to and including untimely death. What's bad about those things? If we're doubting the badness of pain, we may as well doubt the badness of other stuff we don't like and try to avoid, like death. With death, there are some readier answers: you could call it a tragic loss of a just-plain-inherently-valuable individual, but if you don't like that answer (and many people don't seem to), you can point to the grief of the loved ones (conveniently ignoring that not everybody has loved ones) which is... um... pain. Whoops. Well, you could try making it about the end of the productive contribution to society, on the assumption that the dead person did something useful (and conveniently ignore why we tend not to be huge fans of death even when it happens to unproductive persons). Maybe we've just lost an anesthesiologist, who, um.... relieves pain.
And... what, if anything, is bad about pain?
Your standard-issue utilitarianism is, among other things, "hedonic". That means it includes among its tenets hedonism, which is the idea that pleasure is good and pain is bad, end of story. Lots of pleasure is better than a little and lots of pain is worse than a little and you can give these things units and do arithmetic to them to figure out how good or bad something is and then wag your finger or supply accolades to whoever is responsible for that thing. Since hedonists are just as entitled as anyone to their primitive notions, that's fine, but it's not much help to our question. "It is a primitive notion of my theory" is the adult equivalent of "it just is, that's all, your question is stupid!" (I don't claim that this is never an appropriate answer. Some questions are pretty stupid. But I don't think that one of them is...)
...what, if anything, is bad about pain?