“If you’re a Christian, sex before marriage is a sin.”
Its a sin if you’re not a Christian as well.
Some forms of sex are always wrong, others made right by contract. I’d like to see the law allow polygamy, contracted consorts and prostitution. But better to outlaw them, and discretion and privacy be their shield when necessary, than to allow and tolerate in law a general sexual licentiousness.
Let’s outlaw lying and coveting, too.