"You can't legislate morality." I disagree with this in the way it's usually meant, because every law is describing what is right and wrong to do. However, I could use the same sentence in a different way, and fully agree with it. I agree with the idea that "you can't legislate morality" if by that you mean that a person can follow laws and still be immoral.
Laws are often only action-deep. They do not necessarily penetrate to thought-depth. A person can outwardly obey while inwardly rebelling. Obedience can be carried out with the wrong motivation.
While we're on the subject of the law, I think that humanity as a whole will always outpace manmade legislation's ability to guide their actions. The one being pursued has more options than the one pursuing him.
Also, I've noticed that some laws can be atrocious, life-gnawing ogres that strangle productivity. But not all law is like this: God's Law heightens productivity. Why the difference? Maybe because God knows what he's doing, and legislators don't.