Natural Family Planning cannot be intrinsically illicit because it only involves periodic continence. Therefore, if it is nonetheless said to be wrong, then so is abstinence itself.

Now, if it is not intrinsically illicit, it follows that there may be some circuмstances in which it is permissible. There must be truly grave reasons for its practice though, and it can frequently happen that couples err on the wrong side, lacking the prudence, and pastoral guidance, to judge correctly whether their situation really necessitates recourse to it.

It also hardly bears repeating that a contraceptive mentality, which intends to deliberately frustrate the end of sɛҳuąƖ relations, would in and of itself be sinful. But if that is not intended, with us being open both to the working of nature and the gift of God, then one may abstain, either periodically, or totally.

Casti Connubii, which Dimond attempts to explain away,really speaks for itself.

Nor are those considered as acting against nature who in the married state use their right in the proper manner although on account of natural reasons either of time or of certain defects, new life cannot be brought forth. For in matrimony as well as in the use of the matrimonial rights there are also secondary ends, such as mutual aid, the cultivating of mutual love, and the quieting of concupiscence which husband and wife are not forbidden to consider so long as they are subordinated to the primary end and so long as the intrinsic nature of the act is preserved.

This respects natural law, our Creator's design of our bodies and His purposes for our lives. Between NFP and contraception, there is no possible ground for any comparison, one only for stark contrast.

Still, it is the doctrine of Pope Pius XII as well, and I'm afraid that Peter Dimond, inspite of his attempts, really has no legitimate way around that. Either he should recant his own position, or take it to its logical conclusion, that Pope Pius XII is a heretic (and even, as he says, are most sedevacantist groups today), which is evidently absurd. After all, any wayward utterance by a Pope after Pius XII is enough to prove him a heretic, in Dimond's eyes, and one heresy is enough in fact to make a man a heretic, but he looks the other way here.