Goodison_Lad said:
Legal systems are based on the assumption that free will does exist and that people, generally, are not operating merely deterministically.
Er... no. That's exactly wrong. It only works
because it's a deterministic system: because we
can have a causative effect on people's actions. If there was no causation, people would make decisions independent of whether it
caused them suffering. But because the causation chain is not broken, having and enforcing law continues to work.
Just like any other organism, we change our behavior in light of new information as long as that information passes a threshold in our emotional significance detectors (probably mostly in the amygdala and basal ganglia).
The basis for mitigation is where it judged that free will has been significantly compromised, perhaps to the extent that it was completely absent – mental illness, intellectual impairment, duress etc. Society considers that responsibility and free will are two inseparable sides of the same coin.
No, society doesn't care about free will, only responsibility. All society is, is a bunch of individual voices that want safety and security for themselves, so they don't like people engaging in risky behavior around them. It's really quite normal (especially in mammalian organisms) to have some kind of system that eliminates cheaters, for instance.
What we call mental illness, intellectual impairments, duress, etc, are all examples of when executive function is not dominating prediction and decision measures in the brain. When executive function is broken, people do not care about participating in social acceptance. For instance, frontal lobes complete wiring until between age 3-5, when toddler's start caring. The next major finalization comes in the early 20's with myelination, which finalizes the circuit dynamics in the frontal lobes. This gives the organism a long sample-time while the circuits are still plastic to figure out, negotiate, and even create new social rules and paradigms.
When we get frontal lobe damage or deterioration of any sort (whether from traumatic injury, disease, or other morphological or development abnormalities) we care less about what society thinks. The most famous case of this is Phineas Gage, but there have been countless examples since. Rather than seeing them as lacking free will, we can see these people as having broken their detector/predictor mechanisms for social instances.
I think it's best to distinguish between free will, which is a supernatural idea that some force acts independent of cause and effect, and will power, which is the ability for an organism to execute it's needs/wants (determined from biology and environment). Willpower definitely exists and it's how we judge responsibility.
If somebody always wants to kill you, they are responsible. But if somebody has a disease where there arm swings around wildly at random times, we don't consider them responsible. This is independent of whether the system is deterministic or not; it's only a matter of which system is dominating interactions in the organism.