Most priests don't like to sit around thinking about women's temperatures, fertility periods and cervical mucus. And priests certainly don't feel comfortable talking about these things with men and women who come to them for marriage counseling. That's why there are NFP practitioners. After the priest makes Church teaching clear, he can refer couples to NFP programs for the medical nitty-gritty. The baby is born with his nose pointed at Heaven.
Baptism activates the controls.
Every creature has its being determined by the Creator and does the things proper to it. A human being's nature is to know and love God and to be happy with him forever. If he makes choices that go against his nature, he will probably be miserable on earth, and he will certainly thwart his ultimate goal. This is true whether or not he agrees with God on what his human nature is. He can accept his nature and make choices to enhance it-or he can ignore his nature and degrade himself.