I wish the Roman Catholic would understand they practice birth control via NFP.
So are you here to talk about Italy’s population decline or just take shots at Catholics? Nevermind. I know what the answer is.
The difference? It's the difference between respectful cooperation with the inbuilt design of sex and fertility, vs. overriding and disrespecting that design.
To use an analogy: temporary abstinence (NFP) is like a respectful silence. Contraception is like talking and lying.
NFP requires acceptance of and acting harmoniously with the God-given design which links intercourse and fertility. "A time to embrace,and a time to refrain from embracing."
But contraception, by contrast, is actually an act of perversion, like Onan's sin. It's going through the motions, while altering it, impairing it in some way so that its natural fruitfulness, what would be the natural outcome, is sabotaged. The Bible says what Onan did was evil, and God slew him.
NFP could be used with a selfish attitude. But that's a separate issue: the sin would be the selfishness, not the abstinence in itself. I've actually never known couples who NFP it for trivial reasons. It's typically used for health considerations, giving an exhausted or fragile mom a break from too-frequent pregnancies, or using NFP for baby-spacing, not baby-refusal.
I would wager that a lot of couples, without consciously choosing this as a "method," do find themselves temporarily abstaining when a pregnancy would be a seriously bad idea, e.g. the family loses its income and its health insurance because of job loss. They're hoping and praying this does noit last long!
People laugh and mock when they hear about NFP couples having seven kids, but that's not "method failure." It's usually method-success: they spaced their generous number of kids in way that shows wise sexual stewardship. Extended breastfeeding often achieves the same thing.