Of course, that doesn’t mean that a government *necessarily* must legislate all morality. It is immoral for Catholics to skip Mass on Sunday. I don’t want a civil law against it though. Similarly, the fact that states *can* legislate morality doesn’t mean they always do. Often states legislate grave evil by the exercise of raw power. When they do, Augustine is perfectly right to say that an unjust law is no law at all. We are, in fact, morally bound to resist laws contrary to the law of God.
Knowing which laws those are, and what the law of God is in a particular situation, is the tricky part.