All questions of sexual morality come down to one basic question: Is this act an authentic sign of God's free, total, faithful, fruitful love or is it not? If it is not, then it is a counterfeit to the love we really desire. We must be courageous enough not to settle for counterfeits.
The Church calls couples to a responsible exercise of parenthood. This could mean the generous and prudent decision to raise a large family or, because of serious reasons to do otherwise, it could mean to limit the size of the family. However, even if a couple has a serious reason to avoid a pregnancy, the end does not justify the means.
The choice to render an act of intercourse sterile seriously violates the meaning of marital union as a sign of God's life giving love. Abstaining from intercourse does not. In fact, abstaining from intercourse itself can be a profound act of love. Often times, love demands abstinence, and if one cannot abstain, his or her love is called into question.
Natural Family Planning (NFP) is not natural contraceptionm. It is not contraception at all. Never do couples using NFP render thier acts of intercourse sterile. When serious reason to avoid pregnancy arises, a couple abstains during the fertile time. If they so chse, they can enjoy marital union during the God given time of infertility. In thei way, God remains God.