Summary of JP II’s main argument in L&R by Christopher West
When the body is considered something, we apply the “utilitarian principle” (is this useful to me?). This is the essence of fallen sexual desire (lust). When the body is properly recognized as someone, we apply the “personalistic principle” (how can I honor the person?). This is the essence of sexual desire as God intended.
Utilitarianism wants to safeguard the value of pleasure at all costs (this leads to egoism) while personalism wants to safeguard the value of the person at all costs (this leads to altruism).
This is the crux of the conflict between Christian and secular views of sexuality—namely what is to be safeguarded, the value of pleasure or the value of the person. One does not need faith but can conclude from reason alone that the value of the person is superior to the value of pleasure.
Hence, the person should never be treated merely as a means of pleasure, and we must transcend all tendencies of the sexual urge to treat another person in this way (see LR, p. 64).