You do know that the Church teaches that a couple may licitly use NFP to avoid ever having children, don’t you?
As I understand it, it is at least doubtful that a valid marriage could be contracted if a couple, physically able to have children (i.e., not known to be sterile at the time of the marriage), would enter into marriage with the intention never to have at least one child. I do know that it is grounds for nullity.
Nonetheless, if they can in fact validly marry, they would have to use NFP (unless they are resolved to live in a Josephite, i.e., sexless, marriage). They could not licitly resolve to contracept permanently, nor could either or both spouses submit to sterilization in advance of the marriage.
I know the question “what kind of reason would they have to have?” has varied potential answers. The teaching of the Church, at least up to and including
Humanae vitae, was that it had to be a “grave” or “serious” reason. Pius XII was the first to address the issue explicitly; as I said earlier, contraception (or, at least, modern scientific means) really did not exist prior to the 20th century. Some are now saying that it only has to be a “just” reason. I might be understanding some to say that “as long as they are using NFP, their reason is not to be questioned”. Whatever. (I think the time may have arrived for a papal encyclical on the licit use of NFP, but that is not my decision to make.) Grave danger to the life or health of the mother? Grave psychological issues? Genetic issues? Just don’t want a child, “not cut out for it”? (I would draw the line somewhere before “global warming” and “it is nobler and more self-giving to adopt instead of having your own children”, but that may just be me.)
I would then have to ask “OK, what if NFP fails? How will that affect you?”. Again, and this is just me, I have to think that it might be better not to get married in the first place. Avoid the risk entirely.
“But we want to get married!” I understand, but the cold hard truth of life is that sometimes we want things that we cannot have, or should not have. If you go ahead and get married, there is the risk, however remote, that you will have a child you don’t want. What then?
If there arises a situation, once actually married (again, life or health of the mother, discovering a genetic issue, etc.), in which the couple cannot think of having a child, despite having intended to when they got married, then you have two choices, NFP or abstinence until after menopause. Again, the question, “OK, what if NFP fails? How will that affect you?”. Something to consider.
And I have mentioned this previously, but what of those instances where a couple finds themselves physically unable to have relations anymore? The husband gets injured. (I think the reader can fill in their own details.) Or the wife has some kind of similar injury. (Ditto.) Or one of the partners gets cancer and has to have something removed that renders sex impossible. The other partner has to abstain involuntarily. It happens. Unfortunate, tragic, but it happens.
