(...) it wouldn't be terribly surprising to me if some set of people did have poor reactions to certain types of external constraint independently of their physical consequences, (...)

Yes, I was commenting on this at the same time. The mental perception of restrictions, or the mental perception of absence of restrictions, can become a direct brainwired value through evolution, and is a simple step enough from other things already in there AFAICT. Freedom itself, however, independent of perception/observation and as a pattern of real interactions and decision choices and so on, seems far too complex to be something the brain would just randomly stumble upon in one go, especially only in some humans and not others.