I mostly came about this view by thinking about the approach those two camps take to the justice system. The conservative viewpoint on criminal punishment is that it should be punitive; if we make a punishment strong enough and we're "tough on crime", people will stop committing crimes. Criminals lack the willpower to make the right choices. The liberal viewpoint, on the other hand, stresses reformation and changing the person to be different. This is why they tend to be softer; it's not about second chances so much as it is about changing the person into someone who doesn't engage in criminal acts. People can be changed, not through acts of will but by conscious shaping by outside forces.
Another point of contention between liberals and conservatives is what some people would derisively call the "nanny state". This applies to things like gun control, drug enforcement, health insurance, safety protocols, and so on. Free will also explains this difference; liberals believe that people are literally not in control of themselves. Taxes on alcohol and cigarettes and bans on most other addictive drugs result from the belief that addicts are not capable of controlling their actions; the brain is a feedback control mechanism, and restricting the inputs results in different outputs. But for the conservatives, this is more a matter of will - if you don't want to die from lung cancer, you should stop smoking. If you don't want to get fat, stop eating so much. If free will exists, and humans are under their own agency, then these are personal failings rather than the result of outside conditions.
And finally, there comes the issue of gay rights. Liberals would have you believe (in the strong form) that homosexuality is something that you're born with or (in the weak form) something that occurs because of uncontrollable environmental factors. Conservatives will say that it's a choice. What more needs to be said on that issue?
It has long confused me why the conservative cause marries two seemingly different ideologies. Christian conservativism stresses a restriction on immoral things, while the free-market ideologues espouse the theory that people must be free to choose. Why should I be free to pay my workers a fair but unjust amount of money for their work, but not free to buy a magazine with lewd images in it? For me, this seems an inherent contradiction within the party. It seemed at first that there were just two groups that bound themselves together so as not to split the vote, another unsatisfactory result of the two-party system. Then I thought that perhaps this was too cynical, and there had to be some thing which bound them together. I now think that this binding trait might be philosophical.
If free will does not exist, then the market is going to behave in certain ways depending on what all the variables within the market are, and what restrictions are placed on the market by both technologies and governmental interference. In this way, the market is no different than anything else in the universe. It is therefor in the best interests of the people (embodied in the government) to restrict the market in such a way that it does good things for the people (in the form of new technologies, a good distribution of resources, health and safety for workers, etc.) instead of bad things (pollution, child labor, defective products).
However, if free will does exist, then the market is instead determined by how the actors in the market choose to behave. Companies will stop polluting because they are good and honest instead of because they have incentives to stop. If you believe in free will, then I think you almost have to believe that people are by their nature good, or if not that, then at least you must believe that good will prevail in the end. So perhaps the lack of restrictions on the market show that while individuals are not to be trusted in the area of personal choices, large companies are to be trusted on large issues.
Perhaps I'm simplifying the issues too much.