Right, but isn't that the indication that NFP is a very silly and primitive, deceitful "method" that should not be used?
Only if you also think that because foot travel is not an efficient way of moving you should never walk anywhere. Where do you get "deceitful" from? I don't even know why you call it a "method" - it is a method, since people actually use it as a form of birth control; it isn't a figment of one's imagination.
An act that keeps people from sin, yes. A "concession," of sorts: if you are weak, then, well, do the "monkey business" with your wife in strict moderation, so that you will use your "mojo" there, instead of going to whores; but even better, be strong, be a virgin.
Anything that keeps you from sin is good, dude. That doesn't make it a concession - humility isn't a "concession," fasting isn't a "concession," avoiding whorehouses isn't a "concession," they're positive things that one can do to make themselves better human beings. Anything that helps you avoid sin is a positive thing to do to enrich your life; hence, saying that sex in marriage keeps you from sin is also saying that it is a positive influence and a good thing to do. Sex in marriage isn't "economy" - and economy is a concession; economy is bending the standards situationally as a pastoral concession. But sex in marriage isn't that.
(I can't imagine a monastic Father of the early Church, or even a contemporary Orthodox theologian, writing, for example, that truly blessed are husbands whose wives have regular orgasms, because it is good, wonderful, holy thing for a wife to have regular orgasms with her husband.
*sigh* And there aren't any writings about it being a blessing that a man have an orgasm either. Either (a) they weren't worrying about the details, and instead were focusing on the "big picture" of sex, or (b) they don't care. Anyway, why would you look to a monastic father to write about female orgasms? I don't ask you your opinion on omoousios/omoiousios (theological controversies of the 4th century)... It's not your field or focus.
But everyone praises, say, St. John of Kronstadt for openly advertising that he never had sex with his wife - that is supposed to be ah-so-good...)
(a) It was good for him. Just as abstaining from all sexual relations with your wife is probably not right for you, apparently abstaining from all sexual relations with his wife was what was best for him. (b) Of course we're going to say it was amazing - what kind of willpower does it take to abstain from you wife? I'm only engaged, and it's quite a trial! Anyone who displays that kind of force of will (whether it be St. John not having sex with his wife, or St. Mary of Egypt living in the desert all those years, or the Great Martyr St. George the Trophy-bearer enduring countless tortures, etc.) should and will be recognized for that sacrifice.
As a unitive act... sex? No. That's a stretch, I think. That's our modern humanist culture, not Fathers. Or am I wrong?
It's in Genesis for pete's sake! Genesis 2:23-24 (KJV, from bible.com)
23And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man.
24Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.
The fact that sex is a unitive act is presupposed by every Father, Council, and author in our Church. It's a big reason why people are told not to have sex with or marry prostitutes (of either sex) -because now you're unitied with them. It's a reason why each spouse is to be very concerned about the spiritual life and progress of their partner - because you're united with one another, a condition that effects one's journey to salvation. One cannot deny the unitive aspect of sex coming from a Biblical/patristic mindset!
I think what I'm reading in your responses is frustration at the opinions of some people, or bad experiences with this kind of debate. But trust me - things are not as bleak as you're perceiving them!