The discussion brings me back to the observation that, absent the element of free will, existence is strongly deterministic. And along with that goes the choice of being materialist, atheist or whatever along with all sense of responsibility, ethics, etc.
I can't imagine how this follows. Obviously, existence must be non-deterministic if any subset of it is non-deterministic. That is a tautology. As for the political and ethical implications of free will, there are none.
The widely reported cases where a criminal "gets off" due to diminished capacity are simply extensions of legal thinking that is centuries old. We are in an age where the working of the brain is partially understood, and courts are doing what courts do -- judging. Perhaps judging badly in some cases, but that's the way the world works. In any case, free will is dependent on correct brain function, and there are such things organic brain diseases and dysfunctions.