What's the relationship between free will and moral responsibility?

I'm the person who posed this question. Thank you for accepting it for consideration.

For what its worth, I would like to provide the context which led me to pose the question. I read the article at the following link:
http://www.scientificamerican.com/article.cfm?id=free-will-and-the-brain-michael-gazzaniga-interview

I then submitted the following two comments in the discussion following that article. It is the second of these comments that became the basis for my question to you:

=== 1 ===
I used to be quite fascinated by the supposed determinism vs. free will dichotomy, but now I think that the existence of "free will" has the same degree of logical certainty as the statement "I exist", in other words, essentially axiomatic and absurd to question. The obvious fact that it emerges from, and is dependent on a (probably deterministic, albeit of overwhelming complexity) physical brain is of great scientific interest. They both exist, let's figure out the mechanism. The mystery of "free will" is just one aspect of the more general mind-body mystery.

Meanwhile, I do not think this issue has any relevance whatsoever to the issue of moral responsibility and how the legal system should operate. If there were no free will, then the people who are debating those issues have no free will either, their opinions are just as much a deterministic product of their brains, and they are thus not responsible for the penal system they design. A reductio-ad-absurdum.

=== 2 ===
One more point -- I think the concept of free will vis-a-vis the determinism/free will issue is a different concept than the one pertaining to issues of moral/legal responsibility. The former is a metaphysical(?) concept, the latter a psychological concept. Metaphysical free will is binary -- either its true or not. Psychological free will can be a matter of degree depending on factors of nature (genetics) and nurture. Psychological free will presupposes metaphysical free will (see the reductio-ad-absurdum in my previous comment). It surprises me that the distinction between these two free will concepts doesn't seem to be more widely understood.