[St_Thomas_Aquinas]

-—Contraception is wrong because it separates sexual intercourse from its procreative function. Thus, sex can become an end unto itself. The result is mutual selfishness. Making love should never be reduced to a means of relieving oneself-—

I reread the article and realized that the author neglected to mention that the same mentality can be adopted by couples who practice NFP.

Pope John Paul II called this “the contraceptive mentality.” NFP must only be used for grave reasons.

This is where the rubber meets the road.

[Tax-chick]

the same mentality can be adopted by couples who practice NFP

Yes, but it's much, much harder to put into effect without artificial contraception or sterilization.

And even if they do, the couple has not engaged in an objectively sinful act. Not having sex is not a sin against chastity, although it may be a sin against charity (to one's spouse).