However most of it was interesting and well-intentioned. The one gaping hole, though, was in terms of an appreciation of the purpose of NFP. Specifically, most commentators (admittedly from a rather rigorist perspective) seem to think that NFP is principally concerned with avoiding pregnancy. Thus one blogger opined
I would say that these [serious reasons to use NFP] have to exist before one even begins to prepare or attempt to employ NFP. One has a positive duty to have children if married. In order to do this one need only ‘do what comes naturally’. There is no need to consider the number unless one already faces serious reasons dispensing one from this duty.
This is touchingly naive. As one person explained to us, there is no guarantee that a couple can have a baby any time they like, just by "doing what comes naturally". She related her own experience of assuming that she would have a honeymoon baby; she and her husband had to wait four years for said baby to arrive. I'm also reminded of a friend from the UK who is rather bloodyminded about wanting lots of children, when she marries. (She thinks seven would be a good number. She's not even a Catholic!) She's used to explaining this attitude rather defensively but on one occasion she was reminded rather sharply by the mother of an only child that she should accept gratefully what she was given! This woman had one daughter, and would have liked more children but it wasn't to be.
There are a number of versions of NFP out there, from Billings to Sympto-thermal to NaPRO but what all of them have in common (as far as I can tell) is that they are about planning FOR a family by understanding the process of human fertility. This is emphatically NOT about avoiding pregnancy, as the be-all and end-all but is instead about knowing when you can or cannot conceive. Many couples can conceive simply by doing "what comes naturally" but to suggest that this is an unproblematic automatic process is simply nonsense. Male fertility is to some extent a delicate process which is relatively easily upset. (Useful hint from one NFP source - wear roomy underwear! They told us the same thing in school. Also - which I didn't know - avoid plastic seating. It overheats delicate parts that need to be 2 degrees colder than the body core.)
Female fertility on the other hand is an unbelievably complex process, which ensures that MOST of the time a woman's body is intensely hostile to achieving a pregnancy. NFP thus is not about avoiding pregnancy by some sort of devious, "guilt-free" contraception. It is concerned with being able to conceive when we're ready to do so but above all, in terms of conjugal relations, the fundamental principle is one of consistent openness to life, without exception. It also means that if a couple have difficulty conceiving, they have natural and morally unobjectionable means to increase the likelihood of their doing so.
One wonderfully commonsensical NFP stalwart pointed out that her preferred method was one which helped her to conceive, to avoid conception for a time and to recognise & manage menopause when she reached that stage in her life. The whole mindset was one of awareness of, and co-operation with, a natural process. Thus the blogger who suggested that one ought to have "serious reasons" before "one even begins to prepare or attempt to employ NFP" is a bit like someone saying that one ought to have angina pectoris before one attempts to eat a heart-healthy diet or take exercise! In any area of life, a conscientious Catholic should seek to ensure that his body is healthy and working as God intended it to work. Employing super-rigorous categories on the one hand or succumbing to a quasi-contraceptive mentality on the other are not the way to go about this, I'd suggest. Rather a couple who form their consciences rightly, by close and respectful attention to what the Church teaches especially here and here and indeed here can make responsible decisions about the right use of their fertility in order to grow in love and holiness. Not to mention growing in joyful chaos which is, in my limited experience, the hallmark of the Christian family!