After death, we trade the momentary ecstasy of sex for the endless ecstasy of the contemplation of God. We are hybrid beings at the moment, sexual like the animals and spiritual like the angels. The animal part of us serves to redeem the spiritual part of us, and then it will pass away. Now some say that the purpose of sex is procreation. If we were talking about frogs, I would agree.
Frogs play an important role in the ecology they eat insects.
Without frogs, the world would be overrun by insects, triggering some sort of ecological catastrophe. Since frogs die, there must be some way of replacing them, and that way is sex. But sex for frogs involves no virtues and therefore also no vices. Among frogs there are no prostitutes or battered spouses. In the case of frogs, it is true, and I agree, the purpose of sex is procreation.