Despite great progress, we lack even the beginning of an explanation of how the brain produces our inner world of colors, sounds, smells and tastes. A thought experiment with “pain-pleasure” zombies illustrates that the mystery is deeper than we thought.
I'm kind of puzzled why this is seen as a mystery.
We experience pain instead of pleasure when we get damaged because if it were reversed it would be evolutionarily disadvantageous. If I "like" having my hand cut off or having my skin burned off that puts me at an obvious disadvantage of bleeding out or getting infected when my skin barrier is gone and unable to heal.
It sounds less like the problem is that hard, and more like people don't want to accept that they are "zombies" in the grand scheme of things. Our experiences matter to us on the human scale, but we're still just elaborate Rube Goldberg machines of chemistry in the end.
They use an example of designing a "zombie" that reacts to being stabbed like us, but feels no pain -- that programming you give the zombie is pain. It serves the exact same function, we experience pain because those of us that didn't are long dead and gone. It's evolution's "programming" of us, it's a pure biological compulsion.
I mean, perhaps I'm missing the point, but I don't see the difference between us and the zombies.