One often hears people say, 'You can't legislate morality!' People who say this are often people who confuse the genus morality with the species sexual morality. But even upon acquiescence in this genus-species confusion, it is obvious that we can, do, and ought to legislate morality. After all, we have laws against rape, and we ought to have them. Rape is both immoral and illegal, and it is right that it be illegal. The fundamental problem, however, is the confusion of morality with sexual morality. That the two are distinct should be self-evident, hence I won’t spare the reader the pleasure of providing his own examples. But perhaps I should give one example to prime the pump of the reader's thinking. Suppose a woman poisons her husband in order to collect on a life insurance policy. The act is immoral but has nothing to do with sex in the way that committing adultery has something to do with sex.
So the next time someone says, ‘You can’t legislate morality,’ you say: ‘All legislation is the legislation of morality; therefore, if you oppose the legislation of morality, then you oppose all legislation.’ All legislation is the translation into positive law of certain moral judgments we make. The positive law is the law that is 'posited' by legislatures or is part of common law. The contrast is with natural law.
Suppose some positivist identifies morality and legality. (A separate post will show the absurdity of this identification.) Well, if morality just is legality, if the morally permissible, impermissible, and obligatory is identical to the legally permissible, impermissible, and obligatory, then a fortiori all legislation is the legislation of morality.
Of course, from the fact that all legislation is the legislation of morality, it does not follow, nor is it true, that all morality ought to be legislated. In other words, it doesn't follow, nor is it true, that everything morally impermissible should be illegal. (It is also not the case that everything morally obligatory should be legally required.) I would say that drinking oneself into a stupor is morally impermissible, but if it is done in private, the state and its laws should not get involved. (But drive on public roads in that condition, and the whole force and fury of the state and its laws ought to come down on your head.) And I would say that maintaining oneself in good health through proper diet and exercise is morally obligatory, but I don't want to see any laws to that effect. State power cannot be allowed unlimited scope. Leastways, not if you value liberty as every conservative does.