We might indeed ask why God made the same act, which expresses the most intimate love between two persons, an act which also brings forth a new human life. God does nothing by accident. The problem we face is not that our society is obsessed with sex. Sex properly understood requires that we acknowledge God who made it. He enables us not only to grasp the truths of our faith, but to see the meaning and purpose of created realities.
Sex is deeply symbolic.
It is a language that speaks of things beyond sight and feeling. The teaching is not just that it is wrong to have sex in certain circumstances. The teaching is that it is wrong to run away from the full reality of sex. We are not our own. Because we do not own ourselves, we do not own our bodies.