Lust is somewhat a term of art in Catholicism. You may want to take it up with the poster, -- I did not post it. Certainly, a healthy sexual appetite directed at the spouse is salutary. Some may refer to that as "lust". However, technically, "lust" is a disposition where the unitive and the procreative aspect of the intercourse are ignored and only the physical pleasure starts to matter. This is indeed considered sinful. But it is not sunful because the pleasure per se is sinful, but because it is not ordered toward love of God and love of the spouse, even though the spouse is the physical partner.
women are more "receptive" during their fertile times, exactly when one abstains in NFP
NFP is not a method of contraception. In NFP one abstains either during infertile time in order to store up sexual energy for the fertile time, or one abstains during fertile time in order to avoid a pregnancy. However, a valid moral excuse is necessary in order to avoid pregnancy. One who wishes to avoid pregnancy for frivolous reasons is not practicing NFP correctly. Please read the thread form the beginning if you feel like understanding what these valid excuses are. The fact that the female body is naturally oriented toward achieving pregnancy points to the fact that in natural law, any attempt to avoid pregnancy needs a valid morally excuse.
What if you have enough children in your family? For that reason a woman should abstain, for the rest of her fertile life, from sex during the time she is most excitable? And of course it is God's plan that women are the most interested during their fertile time.
I do realize that NFP should not be used to avoid pregnancy except for grave reasons.
I see from your posts that you feel we should have as many children as we can afford, but not to the point of bankrupcy. Or I should say that is God's wish for us.
I guess my question to you, and other very devout Catholics, is what constitutes a grave reason not to have more? I know four to a bedroom isn't a reason. Is the inability to pay for a Catholic school a valid reason? Are stressful pregnancies with much medical intervention a valid reason? What if you are not a very good mother/father and cannot handle more? Or is it up to the individual conscience?
It seems from reading this thread there are so many interpretations of "be fruitful and multiply."
The problem with sexual pleasure is that it is not under the control of right reason due to the disorders of concupiscence.
To will the pleasure of lust as the end of an act (rather than to simply experience it as something that is a part of an act and that impels us to perform it) is to will the surrender of the mind to the sensitive appetites and to turn ourselves away from rationality to slavery to sensible pleasures (sex, food, drink, etc.), and to confuse the means (the inducement of pleasure) with the end (a completed act of marital intercourse).