NFP is morally neutral itself. Its like the difference between bulimia and dieting to lose weight. Both achieve the same goal. But with one the food is partaken and purged, with the other its just not eaten at all. Same outcome, no comparison in methods.
Another example: I may need $25,000 per year to raise my family. I can get a job and achieve the goal, or rob a bank. Same thing is achieved but they obviously are not morally equal.
With NFP you're not "doing it" then preventing pregnancy. You're just not "doing" anything, you are abstaining.
NFP can still be used sinfully and selfishly, with a contraceptive mentality, in violation of scripture. You must have a serious reason to use it.
Sorry, I believe these claims are incorrect, at best. But that's JMO.
Well it's at least nice to know you don't ask your priests to do something you don't do yourselves occasionally.