CNN has an article on the reliably titillating subject of the "sexless marriage," which their experts describe as having intercourse less than ten times a year. One of their experts, Marty Klein, a licensed marriage counselor and certified sex therapist in Palo Alto, California, says that one cause of the problem of sexless marriages is "America's obsession with marriage."
I think this is exactly backwards. I think one cause of the problem of unhappy marriages is America's obsession with sex. Sure, sex is a fun, and is one of the many channels through which married people build up their ties with one another. Human beings are built for strong sexual desire at times, especially men. And you can't beat sex as a way to make babies.
Still, there are many more important things in life than sex. Sex is a normal good of marriage, but its good is not best measured in quantity. The more educated people are, the less often they have sex. This doesn't mean there is something wrong with them. It more likely means that they have other good things to do.
If a couple doesn't have sex much, that could be a symptom of a problem in their marriage. But a low-sex marriage is not a problem in itself.