It seems to me that even if every mental act is wholly caused and determined then law and ethics still function - after all one's awareness of the law and possible consequences, or wish for ethical approval will be mental causative factors, competing with the greed or anger that might impel one to crime."Free will" is needed to regulate human behavior. If you do something bad "deliberately" you will be punished. If it's accidental you will be treated differently. We also give people who are judged mentally incompetent or diseased a pass, but they are usually restricted in some way. I don't think that will change. Only the death penalty and torture become insupportable in the absence of free will and most first world countries at least are already there. The lesser punishments are to protect the population and can be justified IMO without invoking free will. If you kill your spouse, no matter how much he or she deserved it, you should still go to prison for a long time even though it was inevitable.
Myabe they need a belief in free will to work though, even if there is no such thing.
The question is is there some mysterious other thing in the mind that chooses between these influences 'freely' (neither caused nor random but something else?), or is the decision whether to commit the crime the result of the strengths of various causes, maybe operating largely at an unconscious level, and the freedom of decision merely an illusion caused by the complexity and opacity of the process?
I don't know, I'm just not sure what something neither caused nor random is.