This rhetorical question takes many forms:

• “NFP and contraception have the same intention of planning for the good of one’s children.  Both are contraceptive and moral.”
• “How is the conscience of someone who uses contraception different from one who uses NFP?  They both want the same things – the good of the family.”
• “NFP is the same as Contraception because both may aim to limit family size.”
• “Contraception is defined as ‘the practice of or method used in deliberately preventing a woman becoming pregnant as a result of having sex’.  Would this not mean that the rhythm method or other NFP methods would fall under this definition and be at risk of the ‘contraceptive mentality: loss of respect for women and human life, the weakening of family, and population control by governments?’ ”
• “For the same grave reasons that make Natural Family Planning (NFP) morally acceptable, wouldn’t the use of a condom instead be just as moral?  How then is the condom any different from NFP?”
• “Surely you can’t be saying that NFP and Contraception are different because one is natural and the other artificial?   What’s wrong with being artificial?”
• “If every sexual act must remain open to the transmission of life, then NFP is wrong too.” [1] and even
• “In both NFP and Contraception the sperm cells die, so they are the same.”

The recurring theme is that similar goals or effects prove that they are the same, both contraceptive and immoral or both family planning and moral.

The Answer:

Both NFP and contraception have to do with birth regulation but how does that make them the same?

All crows are birds and all eagles are birds but are crows eagles?   Likewise, both Men and Women are human beings but is a Man a Woman?   Or we could point to the hare (genus Lepus) and the rabbit (seven genera) which look similar but are completely different animals.   Or to apples and oranges and even dukus and durians which are all fruits yet different, one from the other.

Good intentions alone without licit methods are insufficient.  If you eat the poisonous mushroom you will die even if you want it to be the delicious, and expensive, truffle.
 

What exactly is this difference?

Although both are used to regulate birth, they do so in different ways.  NFP modifies sexual behaviour to suit fertility while contraception suppresses fertility to suit behaviour.
 

They take opposite paths, and adopting one, either one, means to develop the habits and culture that go with that practice and to turn one’s back on the other – usually with far reaching consequences.

The words themselves imply the paths taken.

“Contra-ception” means anti-conception and is commonly extended to anti-pregnancy and anti-birth, so providing different ways of getting rid of unwanted children in a sex-sparing, anti-life package.
 

Contraceptives are never used to achieve pregnancy, as the term ‘family planning’ should suggest.  They may plan for the good of some children but often at the expense of other children, some of whom may be selected for abortion.  Experience does show in fact that the trends of contraception and abortion are often in direct relation, abortion having being legalised for the purpose of recovery from failed contraception.
 

Contraceptives are not wrong merely because they are ‘artificial’.   They are intrinsically evil because they rupture God’s design of Procreative Love, no matter what good intentions or results we may have for using them.
 

“Natural Family Planning” on the other hand means planning a family, not avoiding one, as married couples decipher their cycles of fertility and infertility in a truly unitive relationship that does not hinder the transmission of life. ‘Natural’ refers to Natural Law, in line with the order of Creation, not to the absence of pills or devices.

While sexual intercourse, unlike nutrition, is unnecessary for individuals, it is a part of married love and commits married couples to the gift of fertility and to accept as many children as they can take care of.   But the Designer has also given them a second gift, the gift of infertility in each cycle, and for grave reasons they can use these infertile days to space or even indefinitely postpone the next child.
 

Like following instructions in the designer’s manual, NFP accommodates God’s design.   If the more serious the matter is, like surgery or flying a plane, the greater the disaster if we fail to follow the manual’s instructions, why should it be any different with the creation of human life and the way God has designed this?
 

Contraception is like locking the door and sending out the rejection, “Don’t come.  You’re not wanted,” but spacing pregnancy with NFP uses the built-in mechanisms of our biology and is like taking the opportunity provided by the Creator of Life to delay the invitation to the next child.
 

Using NFP and using contraceptives are thus different acts, separate from the intentions we may have for using them.  And the act must first be judged independently of these intentions.  This is because you can never do moral evil even for worthy goals or consequences.
 

NFP does not block the transmission of life.   Sexual intercourse is given to procreation but fecundity normally means cyclical fertility until menopause – like a radio is designed to produce music even though it’s sometimes off. NFP is dedicated to this design and the sexual act is not blocked to conception if and when this is possible.  But ‘contraception’ blocks a baby that could have resulted from sex on fertile days.  It changes the design of fecund sex – like using the radio to hammer a nail into the wall.  Abstaining from sex is not ‘contraception’.   After all, celibates are not practising contraception.   Nor is it ‘contraception’ to have sex on infertile days, since conception is not possible then anyway.
 

If we do an intrinsically evil act because there are good reasons for doing it, we would have to say that the evil act is a good thing to do.  To thus misrepresent evil as good makes good and evil indistinguishable and would open the door to all evil acts since no one does anything without a good reason.   Inevitably, this leads to the corruption of conscience and to the increasing inability to make moral choices.