Just as regurgitating would damage your digestive system over time, so artificial contraception will damage your marital relationship. It is intrinsically disordered because it violates your human nature, the nature God has given you. Of course, with calorie-counting, you sometimes fail and gain a pound or two. You accept the inevitable mistake here. NFP is 99 percent effective, but if you conceive, it is a blessing intended by God.
Babies are a joy.
Babies are the result of human love in concert with God, who infuses them with a soul. Babies are miracles. They are what life and marriage is all about. The couple is holding hands and blushing. This is not an easy task.