As I stated before, doctors can't agree on how to quantify pain, and I'm not going to attempt it either. This does not prevent us from comparing lesser and bigger pains, but there are no discrete "pain units" any more than there are utilons.

If you can compare bigger and smaller pains, and if bigger pains can add and smaller pains cannot, you run into this problem. Whether you call one pain 1 and another 1.00001 or whether you just say "pain" and "very slightly bigger pain" is irrelevant--the question only depends on being able to compare them, which you already said you can do. What you say implies that you would prefer 3^^^3 people with a certain pain to 1 person with a very slightly bigger pain. Is this really what you want?