It was about the 20th time this year that I (Richard) had been drawn into a discussion about same-sex marriage — at least the 10th time since the Supreme Court ruling — and I was getting tired of it.

Once, just once, I thought, I would like to hear people discussing the much broader issue of why marriage is now thought of as irrelevant and even undesirable by heterosexual couples.

Which is the bigger issue?

Estimates put the percentage of the U.S. population that is gay at between 2 and 4 percent. Meanwhile, among the 96 to 98 percent of heterosexuals, most seem to be devaluing or completely disregarding the value of marriage.

The largest threat to our society and to our economy is not the way people define marriage, but how enthusiastically and committedly they participate in it. Sadly, and particularly among the millennial generation, fewer and fewer get married while more and more choose the lower-commitment option of cohabitation.

And that huge threat it is being largely obscured and ignored because of the debate over same-sex marriage.

As heterosexual marriage declines and cohabitation increases, children are the losers and society is weakened. One paragraph from our recent book “The Turning” states:

“Cohabitation without marriage produces disastrous statistical results. Cohabiting relationships tend to be fragile and relatively short in duration; less than half of cohabiting relationships last five or more years, and the divorce rates of women who cohabit are nearly 80 percent higher than they are for those who do not (“Cohabitation and the Uneven Retreat from Marriage in the United States, 1950-2010,” Shelly Lundberg and Robert A. Pollak). The major problem with cohabitation is that it is a tentative arrangement that lacks stability; no one can depend upon the relationship — not the partners, not the children, not the community, not the society. In Europe, 8 in 10 people say they approve of unmarried cohabitation. In Scandinavia, 82 percent of firstborn children are born outside marriage (“Nordic Family Ties Don’t Mean Tying the Knot,” Noelle Knox, USA Today, Dec. 16, 2004).”

The justifications we often hear for the cohabitation option amount to tired old cliches like, “You wouldn’t buy a car until you’ve driven it,” or “Well, we plan to make the commitment of marriage after we are sure it is going to work.”

The problem with this logic is that what makes a marriage work is the commitment. Commitment is the start of a relationship that lasts, not the culmination of it. And the commitment of marriage is what lends security both to husband and wife and to the children who join them.

If defenders of marriage are consumed and preoccupied in fighting against same-sex marriage, they are like a sports team that tries to shut down the opposing team but does not score any points for itself. People vigorously fighting same-sex marriage but doing little or nothing to advocate or promote traditional marriage are like a defense with no offense.

The best way to make a difference is to celebrate commitment — the commitment of marriage.

The debate over same-sex marriage will go on, just as the abortion debate goes on. A Supreme Court ruling does not put an end to either issue. Society may still be divided over same-sex marriage in 50 years, just as we are still divided now on the abortion issue 50 years after Roe vs. Wade.

We personally believe the institution of marriage was instituted by God and that he defined it and continues to define it as a potentially eternal union between one man and one woman.

But whatever our personal position, each of us should ask the question of what we should be most concerned about — the emergence of same-sex marriage or the disappearance of traditional marriage.

Richard and Linda Eyre are N.Y. Times No. 1 best-selling authors and founders of JoySchools.com who speak worldwide on marriage and parenting issues. Their new books are "The Turning" and "Life in Full." Visit valuesparenting.com or eyrealm.com.