For human eros is the fruit of the peculiar conjunction of and competition between two contrary aspirations in a single living body: one, a self-regarding concern for one’s own permanence and fulfillment; the other, a self-denying aspiration for something that transcends our own finite existence, and for the sake of which we spend and even give our lives. Nothing humanly fine, let alone great, will come out of a society that has crushed the source of human aspiration, the germ of which is to be found in the meaning of the sexual complementary two that seek unity wholeness and holiness.
Human procreation, in sum, is not simply an activity of our rational wills. It is a more complete activity precisely because it engages us bodily, erotically and even spiritually, as well as rationally. There is wisdom in the mystery of nature that has joined the pleasure of sex, the inarticulate longing for union, the communication of the loving embrace, and the deep-seated and only partially articulate desire for children in the very activity by which we continue the chain of human existence and participate in the renewal of human possibility. Whether we know it or not – and we are already well on the way to forgetting it – the severing of procreation from sex, love and intimacy is inherently dehumanizing, no matter how good the product.
Leon R. Kass – Life, Liberty, and the Defense of Dignity: The Challenge for Bioethics p.157