[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).

[Salvation]

BTTT for your answer....good one.