How does one draw the line between the sort of morality a legal system should

How does one draw the line between the sort of morality a legal system should

How does one draw the line between the sort of morality a legal system should enforce, and the sort of morality the legal system should leave to its own devices? It seems that there are some cases where the law should clearly enforce morality (special laws against child abuse, for example), yet there are clearly other cases where the law doesn't and shouldn't have much to say (for example, the law does not systematically punish people who lie to their spouses, and most would probably argue that it shouldn't). But what is the distinction between the two sides of the boundary?

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