Responsible parenthood is lived out within the structures that god has established in human nature. That is why the Church teaches that couples must not actively intervene to separate their fertility from their bodily union. To do so is to show disrespect for an important gift of the Creator. Sex is a private decisions between to people. Sexual intercourse is not only eminently personal, between a man and a woman, but also has a public and even universal dimension.
Human reproduction orients sexual activity to the future of the world.
The public consequences of sexual intercourse are illustrated by the miracle of birth, and also through the devastation wrought by sexually transmitted diseases. Remember, sexual intercourse radically unites a man and a woman and is the only human act which can worthily bring another person into the world. The Catholic Church does not want couples to have sex for pleasure's sake. Unconditional love is what marriage is all about. This information is available in brochure form.