Let a student announce that law and morality are separate things and that morality can’t be legislated. Many heads will dutifully bob up and down expressing agreement. Bumper sticker philosophy rules.
Normally, one would resort to some great Christian master or other purveyor of natural law arguments to dispel the haze.
But I came across something from Jeremy Bentham, the utilitarian and opponent of natural law, that caught my attention. In chapter XII of his Principles of Legislation, he argued (much to my surprise) that law and morality are part of the same whole.
Run your eyes over this:
Morality commands each individual to do all that is advantageous to the community, his own personal advantages included. But there are many acts useful to the community which legislation ought not to command. There are also many injurious actions which it ought not to forbid, although morality does so. In a word, legislation has the same centre with morals, but not the same circumference.
In other words, some morality can and should be legislated, for morality and law share the same center. I doubt St. Thomas would have disagreed.