Many people ignorantly accuse the Church of teaching that people must have procreation on their minds as a conscious motive in order to engage in sexual union. This is false. To see why, we must appreciate the notion of telos, which in Greek means end/purpose/fulfillment. This applies especially to the two bodily appetites inherent in humans and other animals for the sake of the continuation of life  – life of the individual (eating) and of the species (sex). Secondly, we must distinguish between personal motive and natural end (telos) or purpose.

Just like one need not have nutrition as a conscious motive for eating, one need not intend procreation to engage in the marital embrace. Conversely, like one must respect and not impede the natural end of eating, which includes digestion and nutrition, one must respect and not impede the natural end of sex, which is insemination and (at least potentially) procreation. This is known as the principle of finality: once the act is begun, it may not be intentionally impeded or perverted from its natural end.

Both sensual bodily appetites are for life-giving ends. While love (of self or spouse) and pleasure may be personal motives for either eating food or sexual union, stifling life by bulimia (in eating) and contraception (in sex) impede their natural telos (end/purpose) respectively, and are intrinsically disordered acts. Both bulimia and contraception violate human nature and natural law and militate against human fulfillment. Both seek to separate pleasure from purpose, and in doing so separate love from life, resulting in neither. As such, it is not a stretch to consider contraception to be akin to sexual bulimia.