The teleological end of human life intended by God in the Christian conception is the beatific vision and union with God, not the instant of death. Sin is simply the engagement of actions that thwart this end, which is achieved through fidelity to the law of God and the sanctification of the human soul through theosis. On your point regarding sex, the natural end of sex is directly reproduction. Its why the entire set of sexual equipment biologically came to be. Presuming evolution (sorry creationists ) the very reason sex exists is due to the biological imperative of procreation, with all other aspects of sex (such as pleasure) being entirely contingent, and indeed oriented to serve this end (pleasure existing so that it is enjoyable, thus supporting procreation by making sex a desirable activity). Your assertion that reproduction is a byproduct (in the sense of ends) of sex is simply absurd from a biological point, and from any rational perspective, it is quite clear procreation is the direct objective. Now this applies to morality in the Christian perpective, since Christianity upholds that God created the universe and established within it an order. If the ultimate end of the Christian is to obtain the beatific vision through following Gods law, than acting in harmony with the order of nature obtains a moral character, since the entire definition of morality hangs upon becoming closer to the divine. Ergo what is in accord with the order of God's creation and is in harmony with his will and divine plan is moral, and what is not is immoral. Since God created the universe and its laws, and since sex is biologically in the laws of nature oriented towards procreation, to the Christian it is morally right to act in harmony with the inherent order of nature, and with the natural end of the sexual act as is imperative biologically, within the context of the end of the human being himself to achieve the beatific vision. Your position that what is moral and what is immoral changes on the other hand is entirely predicated upon a worldview which denies the existence of God, and is abject relativism. Likewise it clearly manifests the reality that without God morality cannot exist, since if God does not exist (and man does not have a teleological end in salvation) what is left is pure opinion and no moral conception can be said to be objectively true. This leads logically of course to the nihilistic vitalist rhetoric you have expressed here. The discussion between Plotinus and I however fundamentally hinges on whether the Catholic framework is consistent, which naturally presumes the existence of God with all the accompanying ramifications of that existence.