The abstaining couple that is practicing NFP is acting in such a way that they are not calling upon God's creative act at that time. We cannot imagine God being insulted or dishonored here. The couple is simply not performing an action whose nature is ordained to elicit God's creative act. God is still present, still respected, but no invitation is sent to Him that would invoke His presence in the specific form of His being a Creator of new life. Contra-wise, the contracepting couple, by using contraception, is sending an explicit message to God that His creative presence is not desired.
Sex is, of course, a great gift.
It would be in keeping with humility and restraint that are the appropriate expressions of gratitude for this gift that whenever we engage in sexual intercourse we do not insult God but respect and honor His creative role. There is a real difference between preventing something from being and choosing not to cause something to be . The contracepting couple chooses to prevent a possible person from coming to be . These two relationships, with respect to human life, are morally different. It is not possible to prevent a possible baby unless a baby is about to emerge as a result of a life-giving action.