By Mary Abrahamson   In talking to an older mom awhile back, discussing the trend among young people to delay marriage, my friend said, “Why by the cow when you can get the milk for free?”   I understood, of course, her metaphor.  She was expressing that with extra-marital sexual activity dominating our cultural norm, there was no compelling impetus for a young person to assume the commitment and responsibilities that come with marriage.  This line of thought appeals to our sinful condition.  And to our humanity, in a sense. We are biologically inclined to want to engage in sexual behaviors.  This is a natural and good thing, in its…