No, pain isnt always due to structural or physical damage. That is what functional pain is. In many ways it is much worse than physical pain.

I do not think this hypothesis is correct. What evolutionary purpose would functional pain serve?

To me, it seems it's a theory to compensate for medical imaging technology that has far too low resolution. Doctors hate admitting that they don't know what's wrong, so instead they claim that the patient is crazy in politically correct terminology with an excessive number of syllables.

Structural tissue damage starts at a molecular level that cannot be seen by medical imaging technology. The fascia alone is too thin to be imaged at all, and so is completely ignored.

Biochemists have delineated in explicit detail how tissue breaks down at the molecular level. And they can reverse it. We need to start listening to them more.

There is pretty clear evidence from neuroscience that pain has a significant emotional component. The evolutionary benefit is to having an emotional component is that it makes it less likely that the animal will try to override the pain.

Yes I agree with that theory, but I don't see how that proves that pain is completely decoupled from physical damage, and just randomly happens to some people solely because they are upset or "disturbed".

I never said that.