If you abstain, you are saying no also.
Abstaining is only promoted for pre-marital conditions.
The Catechism of the Catholic Church teaches that intercourse is a meritorious act in the context of marriage.
Natural family planning allows a man and woman to estimate by the Heavenly-ordained course of nature when the best time of pregnancy/not pregnancy occurs. It is not contraception because it is a natural means of reproductive planning. The couple are still open to procreation because pregnancy is stil possible if not properly done.
Anything that creates an obstacle between God and His right to create life when penetration occurs is a moral evil.