Morally acceptable
NFP is the only form of family planning that respects God’s plan for love, marriage, and sexuality. For many couples, this is the overriding reason they are glad to have found it. Every other method of family planning is an attempt to change a person’s fertility as designed by God (i.e., medication to stop the natural process of ovulation, a device to prevent the natural meeting of sperm and egg, a surgery to permanently stop a natural function).
On the other hand, a couple using NFP respects God’s design of their bodies and works within that design instead of trying to change it.