Suppose a woman has a miscarriage, and is advised by her doctor that, if she and her spouse abstains from the marital act for 90 days, it will improve the chances of procreating a live birth.
In this case NFP/abstinence is used not to frustrate or avoid childbearing, but in order to INCREASE THE CHANCES of a successful birth.
Yet if NFP/abstinence is intrinsically evil, this advice could not be followed, and the primary end of marriage would be frustrated.
It is clear, therefore, that NFP/abstinence is not intrinsically evil.
Circuмstances can make it good (promoting the primary end of marriage).
That is to say: Whether one calls it NFP or abstinence, the goal of temporarily avoiding procreation is not always evil.
It is not surprising to me that the Feeneyites here have a problem understanding this, since just as in the case of baptism of desire, what they are really doing is reacting against the potential for abusing the principal, and that reaction leads them in both cases to overreact and condemn the principle itself.