It is perfectly reasonable if an unrivalled leader wants his folks to have at least three children, to raise devout generations and to remain loyal to their spouses: The bigger and stronger the family, the bigger and stronger the country.

All the same, such a wish list could be problematic if the elected majority attempted to outlaw, through man-made laws, what holy books forbid.

President Recep Tayyip Erdoğan regrets his 2004 decision to drop a draft law that would have outlawed adultery. He thinks it is time to discuss making adultery illegal. That reminds of the old joke: “Don’t steal, don’t lie and don’t cheat. The government hates competition.”

Criminalising adultery (or any other behavior) just because the Quran (or any other holy book) forbids it reflects a deeply problematic thinking. Outlawing every sin should then urge a Muslim parliament to make pork and alcohol illegal too, among hundreds of other practices that are not illegal. In the first place, this is not how nations progress: If outlawing the sin would make nations wealthy, prosperous and developed Afghanistan, Pakistan and Bangladesh (with a combined population of nearly 400 million) would not have been failed states, but most countries occupying the top ranks of the UN human development index would.

There are practical problems, too, about illegalizing adultery. How to establish the crime in court? With a new witness system, taken from the Quran, that says one male witness equals two female witnesses?

And which act(s) should be defined as adultery? The Quran, like other holy scriptures, condemns and forbids adultery but does not define what constitutes it. But modern Islamic jurisprudence broadly defines the act of adultery (zina) as “sexual intercourse or a look, talk, touch, or desire that is related or may lead to illicit sexual relations.”

Since Mr. Erdoğan takes his inspiration from Islam’s holy book the legislation he should suggest should be based on the modern Islamic interpretation of the act of adultery. In which case two adults married to different spouses could be prosecuted if they look, talk or touch each other in a way that may lead to illicit sexual relations. Like having lunch in the cafeteria of their workplace? Like giving each other a friendly kiss and a pat on the shoulder?

And what if two adults are discreetly in love with each other but do not go out, talk, touch or have sexual intercourse? How will Mr. Erdoğan’s law enforcement officers catch those shameless criminals? Will the state scientific research institute develop an adultery-metre gauging sexual feelings that constitute adultery between two adults?

And will it be illegal if a man commits adultery with the intention of marrying his second (or third or fourth) wife which is permissible in Islam?

Once again it is the clash of man-made laws of the modern state vs. God’s commandments that force Islamist polity into endless predicaments and unreason.

Good luck, gentlemen.