Comments on the post below have led to yet more intriguing thoughts (I love this kind of discussion. Everyone has time to think things through and actually say what they otherwise might not think of until the discussion was already over.)
I implied below that some of the reasons people choose for not getting married and/or having children were selfish. As others have pointed out in comments, people may also do so for unselfish reasons or get married and/or have children for selfish reasons. Quite right. No one has a monopoly on selfishness or selflessness.
But that doesn't mean the character qualities have no connection whatsoever to the natural course of family life. Rather the relationship is more complex and subtle, but ultimately very important.
The end goal of everything we experience, good, bad, and indifferent, is for us to know God and be like Christ. With this goal, God has set up the world to teach us these things. The way He has hard-wired human beings for family life is one key way He both reveals himself to us and teaches us to be more like Christ. That's why He constantly uses it as an analogy: "You have been like an unfaithful wife." "I pity you like a father pities his children." "I will remember you even more than a mother remembers her nursing baby." Then he turns the analogy back to us and says, "Now you live in your lives after the Great Pattern of my love."
Each area of family relationships is designed to teach us things. For instance, being "in love" was always a term I despised and would have avoided at all costs as meaningless emotional blather. Then I read someone--I think it was Elisabeth Elliot--define it as "seeing another person the way God meant them to be." That made sense. Some people go overboard into a love-is-blind situation, but if you keep your wits about you and both genuinely love as you are "in love," you know the one you love has many flaws yet, but your desire to see them become the person they were made to be overrides that.
It's like God gives, at least to some, a chance to glimpse things from His perspective. That glimpse then provides us with something to hang on to during the times when the realities of living with a fellow sinner overshadow the grand vision we had at the first. Because in reality, that perspective is the one we need to learn, not just with our spouses, but with everyone.
The love between husband and wife, however, doesn't necessarily teach us the sacrifice that love requires. For most of us, investments in our spouse pay off rapidly. We help and are helped. We receive back in similar kind what we give. When we do have to give in an area where our spouse doesn't give anything back, it's hard to do.
But then come babies. For nine months you haven't even seen this person, yet they rearrange even the most intimate aspects of your life. For weeks on end you care for their every whim, devoting yourself around the clock to their needs. And then one day, they give you the faintest glimmer of a smile, and you go bonkers with delight. Why? Because somehow God puts into new parents the willingness to serve their children and not get anything back. The slightest glimmer of appreciation seems like ample repayment.
These natural drives are amazingly powerful. But they are only natural. Left to themselves, they quickly either fade away or turn to poison--and the stronger the love, the stronger the poison: jealousy, nagging, possessiveness, manipulation, idolatry. In The Great Divorce, C.S. Lewis has some insightful passages where a woman's love for her son is the very thing that keeps her from heaven, whereas a man's lust, submitted to God, becomes the very thing that carries him there. All natural desires are good or bad only as we allow them to draw us closer or farther away from God.
The purpose of the natural drives in family life is rather like those little letters made of dotted lines at the top of penmanship pages. They are meant to provide us with a practice area for learning the genuine love that God desires us to show. We don't keep writing on dotted lines forever--eventually, we have to learn the shapes on our own. Similarly the natural passions by themselves aren't enough to sustain us through the difficulties of life. But they help us learn the pattern, if we look at them as revelations from God and submit them to His sovereignty.
It's quite possible to learn Christ-like love outside of the family, just as it's possible to learn good penmanship without ever tracing anyone else's letters. It's also quite possible to be married and have kids and never learn a thing about love, just as there are plenty of people who started out with good patterns but now have deplorable penmanship. Yet it's no accident that there are traceable letters in penmanship; nor should we ignore the connection God has designed between our families and the Family of God.