He starts from a graceful exposition of Natural Law doctrine:
The ultimate foundation for our responsibility towards the earth rests on our beliefs about creation. The earth is not simply our possession which we can plunder according to our interests and desires. It is rather a gift of the Creator who has designed its intrinsic laws and with this has given us the basic directions for us to adhere as stewards of his creation. The fact that the earth, the cosmos, mirror the Creator Spirit, clearly means that their rational structures which, transcending the mathematical order, become almost palpable in our experience, bear within themselves an ethical orientation. The Spirit which has formed them, is more than mathematics, he is the Good in person, using the language of creation, and points us to the way of right living.Unfortunately, that's where Benedict takes the traditional wrong turn, with the overly simplistic claim that bonding in heterosexual matrimony is a universal moral imperative. His analogy to forest conservation calls to mind the evolution of that science. Where we once approached conservation with the idea that we should protect the trees from all threats, we have since come to realize that some "threats", including fires, are actually a part of the natural process, essential to the long-term maintenance of the forest ecosystem. If we were to apply Benedict's philosophy to forest conservation, we would take every possible step to put out forest fires (including naturally caused ones), and we would do all we could to ensure that every acorn that fell had the opportunity to germinate into a full-grown tree. But this would be completely unnatural. In the delicately balanced complex ecosystem, undergrowth keeps too many acorns from sprouting too densely, while occasional fires keep the undergrowth from getting out of hand and allow certain other plants to germinate. We understand this now.
Since faith in the Creator is an essential part of the Christian Credo, the Church cannot and should not confine itself to passing on the message of salvation alone. It has a responsibility for the created order and ought to make this responsibility prevail, even in public. And in so doing, it ought to safeguard not only the earth, water, and air as gifts of creation, belonging to everyone. It ought also to protect man against the destruction of himself. What is necessary is a kind of ecology of man, understood in the correct sense.
With such an understanding in mind, the more rational approach for a "proper ecology of man" would be to recognize that man thrives in a complex society where different people make different contributions using their different talents, and not all people are called to the same end. With regard to the propagation of a societal species like ours, there is no justification for the claim that each and every individual has a duty to mate and reproduce. Many mate and reproduce, but some make other contributions to the furtherance of humankind, like teaching, caring for the sick and infirm, creating works of art, progressing science, and otherwise supporting families and society. Need I mention priests? It is really the height of blind arrogance that a celibate man addressing a curia composed entirely of celibate men could pontificate so obtusely about the moral call of all humans to mate, with such a glaring counterexample right in front of him. And as if this weren't enough, Benedict, in his 4th point of this very speech, cites 1 Corinthians 12. That whole chapter is an eloquent conceit on the Church as the body of Christ, with each member working with different gifts, just as each part of a body contributes differently to the whole:
If the whole body were an eye, where would the sense of hearing be? If the whole body were an ear, where would the sense of smell be? 18But in fact God has arranged the parts in the body, every one of them, just as he wanted them to be. 19If they were all one part, where would the body be? 20As it is, there are many parts, but one body.It defies reason how Benedict can cite this very scripture in a speech insisting that all parts of the body should be reproductive organs.
21The eye cannot say to the hand, "I don't need you!" And the head cannot say to the feet, "I don't need you!" 22On the contrary, those parts of the body that seem to be weaker are indispensable, 23and the parts that we think are less honorable we treat with special honor. And the parts that are unpresentable are treated with special modesty, 24while our presentable parts need no special treatment. But God has combined the members of the body and has given greater honor to the parts that lacked it, 25so that there should be no division in the body, but that its parts should have equal concern for each other. 26If one part suffers, every part suffers with it; if one part is honored, every part rejoices with it.