NFP is contraception
That is all the proof I need to inform me that you have no idea what you are talking about.
NFP is refraining from engaging in sɛҳuąƖ intercourse. Period.
Contraception is engaging in sɛҳuąƖ intercourse while using artificial means to prevent conception.
So, let me ask you:
If I did not engage in sɛҳuąƖ intercourse with my wife last night, did I practice contraception?
NFP (NBC I call it) entails refraining from the marital act -- which is not intrinsically evil (as you point out).
ABC is obviously intrinsically (and materially) evil.
NEVERTHELESS, NBC is extrinsically or formally evil (i.e. based on extrinsic factors such as motivation) since the INTENT is to control the number of children, i.e. since the INTENT is to partake of marital relations while excluding procreation. In so doing, you are by your intentions trying to divoce the marital act from its intended purpose or end.
So it amounts to the same thing, really, though in the case of Artificial Birth Control, it's intrinsically evil, in the case of Natural Birth Control, it's extrinsically evil.
Very few people who practice NFP actually apply the "grave reason" exception. I personally find the "grave reason" thing problematic. For if NFP is immoral, then grave reason represents ends-justifies-the-means moral theology.
If you have sufficiently grave reason, then it would be sinful to have marital relations at all, for since NFP isn't 100% foolproof, you would be risking the life of your spouse in so doing (the only sufficiently grave reason that could POSSIBLY justify NFP). Unfortunately the "grave reason" thing becomes a slippery slope, leading to people spreading out children because of the psychological hardship of having so many, and limiting the number of children because they could not afford to send them all to Ivy League schools.
If you have grave reasons not to conceive, then (complete) abstinence IMO is the only acceptable route to take. If your spouse disabled or gravely ill, etc., you have to practice abstinence. Justification for NFP seems to be predicated on some sense that people have a God-given right to sɛҳuąƖ gratification. Which principle was enshrined at V2 as the "unitive end" of marriage, which is euphemized from what my wife calls the "recreative end". Unitive is bull-speak for a right to have sɛҳuąƖ pleasure in marriage without have to subordinate that to the procreative end of marital relations.
So Raoul is quite correct in calling NFP contraception--the attempt to limit or stop conception while at the same time engaging in marital relations. I dislike the euphemism of calling it "Family Planning" when it's natural, but "Birth Control" when it's artificial. In both cases it's "Birth Control". So there's Artificial Birth Control (intrinsically--materially and formally-evil) and Natural Birth Control (extrinsically--formally--evil).