Free will and crime

Let me begin with a disclaimer.
I am not an expert on philosophy, psychology, sociology or judicial process. As a matter of fact, I do not even read very much any more, except for the odd business or trade journal. As an enthusiastic teenager I struggled through some Camus, Kafka, Voltaire and various other depressing old buggers, so I could impress people at parties. I also picked up a volume of Desmond Morris' theories on behavioral evolution (mainly because of a picture of a naked woman on the cover) and found it quite fascinating (the theory, not the cover...well actually, maybe the cover too, given that I was 18). But therein lies the extent of my expertise in topics pertaining to free will, causality and evolutionary conditioning. I have no in-depth knowledge of the latest in theories or research in any of these fields. If anyone reading this does, and finds weak spots in my arguments, then I welcome you to poke holes in them. I will not be offended. I wear the tag of 'arm-chair theorist', if not with pride, then at least with comfort.
That being said, here's my burning, though not novel, question of the day - does free will exist? And if not, how then can we hold any criminal accountable for his crime?
Given that the brain is eventually a biological machine, conditioned by generations of evolution, moulded by individual experiences and full of genetic quirks, can its owner really be responsible for its vagaries?
If you were short or puny as a child, then chances are that you will grow to be crafty and passive aggressive. Those were the qualities you needed to survive while growing up among your peers.
If you were exposed to violence at home while young, then you will probably have a greater tolerance for giving and receiving it when you are older.
If you have the misfortune of contracting Lyme disease, then you are likely to experience sudden bouts of uncontrollable rage.
If you come from a primitive society, you are likely to be accustomed to practices and cultures that are shocking or even criminal to a more progressive observer.
Overall, every facet of who you are and how you behave today can be explained by what you were born with and what your circumstances have done to you. Free will, the ability to choose between one option and another and thereby control your own destiny, is an illusion.
People take every decision to maximize their own self interest at the time, to the best of their knowledge. Your most altruistic act of self-sacrifice is done with an inherently selfish motivation, in that you value someone else's happiness above your own. Similarly, your most despicable deed is done with the knowledge that the gratification it brings outweighs the risk of getting caught or any potential weight on your conscience. In short, when taking a decision on how to react to a particular situation, a person really has just one option - the one that maximizes his or her current, perceived self interest. It’s the one option that ensures that the actor is best obeying all the pre-programmed rules of genetics, pre-conditioning and past experience that wire his brain. It’s just like a computer program that can produce only one result with the exact same set of inputs. So where does independent thought come in?
I realize that this is a tough pill to swallow. The illusion of free will is so persuasive that it is hard to see past. But if we drop our egos for a second and examine the facts - it seems pretty self evident. The workings of our brains are eventually explained completely by physics, chemistry and biology. Neural networks, synapses and memory cells are all measurable physical entities. Their functioning controls who you are, and together they define your individuality. If it were possible to build a supercomputer capable of measuring the exact position and velocity of every particle in the universe, then it would also be possible to map out your brain perfectly. It would map every cranial bump and every misfiring neural receptor. This supercomputer would therefore predict how your brain would react to any given situation. Since this computer would also know your environment perfectly, it could also compute every facet of your life from this point out - always predicting your decisions, their ramifications and the decisions you take based upon your new circumstances. The fact that such a computer does not exist, does not take away from the fact that your life is already mapped and that you do not have the capacity to impact your own destiny. Omar Khayyam's moving finger has already written everything that there is to write. You are left to simply follow your script.
Now, for the second part to my argument; given that there is no scope for individual free thought, why then should any action resulting from your pre-programmed brain be punishable? If the criminal has no control over his actions, then what purpose does punishment serve? Other than the motivation of revenge, as per the ‘you-hurt-me’ ‘I-hate-you’ ‘I-am-happy-when-you-suffer’ school of thought, can punishment for a crime achieve anything positive?
In fact it can. It deters the crime, even if it is unfair to the hapless criminal. The fact that a murderer is not personally responsible for his actions, does not in any way decrease the severity of the crime itself. The crime must be punished and its occurrence diminished, regardless of the helplessness of the criminal. The fear of punishment will influence the general environment surrounding other potential criminals and therefore help to prevent future crimes.
I'm obviously not the only person who believes that punishing those who cannot control their actions is unfair. The judicial system does allow for leniency for crimes committed by the mentally unstable and by those in the grips of a 'temporary insanity', and the list of what qualifies as a mental disease seems to increase every day. Road rage was recently ruled to actually be a medical condition caused by "intermittent explosive disorder".
I am simply advocating that the argument be taken through its next logical steps. Temporary insanity suggests a condition in which a person is not in control of his or her own actions for a short time. I am merely pointing out that people are never completely in control of their actions. A fit of anger, bad circumstances, poor values imparted during childhood - all these factors can cause a person to commit an act that a rational, well balanced individual would be incapable of. Why should common criminals be treated differently from people who have "medically certified" mental diseases? In my opinion we should completely separate the mental state of the criminal and the nature of the crime. The two should be addressed separately. All criminals should be sympathized with, as secondary victims of crime, while crime itself should be treated as an evil that should be eradicated. If that means punishment for the perpetrator, then that is unfortunate but essential.
Well, I suppose I have rambled on for long enough, but let me close by saying this. If losing complete control of one’s decision making power is considered grounds to declare one insane, then we are all insane. However that does not mean that we should ignore actions that are detrimental to us as a society. Punishment maybe unfair to the criminal, but it remains a necessary disincentive to crime.