Here are 10 from the Family Research Council.

The list:

1. Children hunger for their biological parents.
2. Children need fathers.
3. Children need mothers.
4. Evidence on parenting by same-sex couples is inadequate.
5. Evidence suggests children raised by homosexuals are more likely to experience gender and sexual disorders.
6. Same-sex “marriage” would undercut the norm of sexual fidelity within marriage.
7. Same-sex “marriage” would further isolate marriage from its procreative purpose.
8. Same-sex “marriage” would further diminish the expectation of paternal commitment.
9. Marriages thrive when spouses specialize in gender-typical roles.
10. Women and marriage domesticate men.

The eleventh one they missed is that a husband’s leadership is beneficial to a woman because it gives her direction and balances her emotional highs and lows. It’s not politically correct to say what women need from men in marriage, but it’s true. Just like men, women have weaknesses that can be corrected and compensated for by the opposite sex. The twelfth one they missed is that same-sex marriage is incompatible with religious liberty, as recent court cases have shown.

Anyway, here are the details on #7:

7. Same-sex “marriage” would further isolate marriage from its procreative purpose.

Traditionally, marriage and procreation have been tightly connected to one another. Indeed, from a sociological perspective, the primary purpose that marriage serves is to secure a mother and father for each child who is born into a society. Now, however, many Westerners see marriage in primarily emotional terms.

Among other things, the danger with this mentality is that it fosters an anti-natalist mindset that fuels population decline, which in turn puts tremendous social, political, and economic strains on the larger society. Same-sex marriage would only further undercut the procreative norm long associated with marriage insofar as it establishes that there is no necessary link between procreation and marriage.

This was spelled out in the Goodridge decision in Massachusetts, where the majority opinion dismissed the procreative meaning of marriage. It is no accident that the countries that have legalized or are considering legalizing same-sex marriage have some of the lowest fertility rates in the world. For instance, the Netherlands, Sweden, and Canada have birthrates that hover around 1.6 children per woman–well below the replacement fertility rate of 2.1.

I chose this one because I wanted to comment.

I think it’s common today for men and women to not put the production and development of children at the center of their marriage plans. They are not working a financial plan to prepare for children. They are not developing the skills they need to mentor and nurture others. They are resentful of any demands placed on them that restrict their freedom. And they want marriage to be about fun and self-fulfillment. This is not compatible with children, however. And that’s the point. The more we redefine marriage to be about adult selfishness – first with no-fault divorce, then with same-sex marriage – the less emphasis there is on the pre-marital preparations for making and raising children.

If you want to know what you should be doing with your life before marriage, then think of the process of having children and raising children. Think of how much it costs, what skills you will need, and how your character has to be trained. Many of the things that you see young people doing these days – binge drinking, hooking up, running up debt, cohabitating, avoiding things that are hard to do – are not preparing their character for the responsibilities, expectations and obligations that people face when they have children.

Suppose you have a friend who is not good at driving a manual transmission car or not good at weight lifting or not good at doing apologetics – are you able to help them do it, or are you incapable of taking responsibility? If you can’t take responsibility for helping an adult, you certainly can’t take responsibility for a child – children are much less capable. Now are you able to say no to doing things for your own happiness? If you are not able to give up your own happiness – and this is a thing that gets easier as you practice more – then you’re liable to look on your duties to your children with resentment – that you are being “manipulated” into it. You don’t suddenly learn how to put up with children just by walking down the aisle at a wedding. It takes training to get good at being generous with your time, money and effort. It takes practice.

In fact, a smart man who is courting a woman would be trying to get her to practice the behaviors of a wife and mother before he marries her. And the same for a smart women who is being courted by a man. For example, a man has to comfortable giving things to the people around him – he can’t be resentful about it. Even when he doesn’t particularly like those people, he has to focus on their needs, think about where he is trying to lead them, and then work a plan to provide for their needs so they get where he wants them to go. If a man doesn’t like the feel of caring for others who may not be grateful – or who may even hate him – then he should take steps to prepare his character to learn to like it. When a little kid says “I hate you!” to his father, who is paying thousands of dollars for him to grow up, it’s not an easy thing. Always being selfish before you marry is not good preparation for what children will demand of you. This is something I struggle with personally – being content to invest in others who turn out to be ungrateful, and even destructive.

So I think this focus on parenting is a wonderful way for people to work backwards from the goal (healthy, happy, successful children) to the interim tasks and required skills. It helps us to get away from thinking that marriage is about us – our happiness, our needs. Unfortunately, not everyone who runs around telling people that they want to get married “some day” is really taking steps to prepare for marriage and parenting right now. Marriage is a commitment to self-sacrificially love another person – however much they change – for the rest of their lives, and to love any children who appear, too. People don’t like to read about marriage and think it through. But just saying “I want to marry someday” is not a proof of preparation for marriage, as the divorce rate attests. To get married, you have to train yourself to think of others, and to do hard things that don’t make you feel “free” or “happy”. There is no path to a successful marriage that does not involve responsibilities, expectations and obligations for husband and wife. It’s not “happily ever after”. It’s hard work!