It is natural law. And men and women throughout the world know innately that it is so. It is not only homosexuality that is wrong. Any sex outside of marriage is wrong. Adultery is wrong.
Premarital sex is wrong.
The central virtue for a healthy society is chastity. Young people should remain virgins until they are married. Husbands and wives should be faithful to each other. Within marriage, a husband and wife are free to enjoy the God-given pleasure of sexual ecstasy. It is one of the great blessings of conjugal love.