NFP is like saying, “Wow, those cookies look great. But sorry, I’m on a diet right now so I better not.”
Contraception is like saying “Wow, those cookies look great. Let me eat them all but then immediately go puke them all up.”
Contraception is sexual bulimia. You seek a natural pleasure, but you frustrate its natural effect.
It seems to me that using artificial sweeteners to make the cookies would be cheating in the same way. You eat fake food to gratify your tongue with sweetness without getting the nutrition (calories) that normally accompany the sensation. The natural effect of eating or drinking is that you are nourished.
Maybe that’s why studies suggest that those who drink diet soda tend to be more overweight than those who don’t. They unconsciously eat more to compensate for the missing calories.