A couple using contraception and a couple using NFP have the same goal; they only use different means. So why does the Catholic Church condemn the on and endorse the other?
Differing means can make a world of moral difference.
Suppose you and I both needed a thousand dollars for some worthwhile cause. You get a part-time job and earn the money. I pull a scam and cheat a poor, elderly widow out of the same amount. See the difference?
The hypothetical couples do not have the same goal. thous both intend in a given sexual union to avoid conception, the similarity stops there. The contraceptive couple is acting directly against the procreative good of their marriage and thereby is setting up a barrier to God's plan for marital union. The NFP couple is cooperating with the natural cycle of fertility and choosing not to exercise the preocreative capacity at certain times. At other times they will use the knowledge gained through NFP to help them concieve. At no time will they act against God's gift of fertility to them. At no time will they treat that mysterious gift as an intruder needing a mechanical or chemical "fix."