Well, you’re talking about the reasonableness of the Church’s NFP doctrine, so here is wisdom: God created woman to have a natural monthly fertility cycle. God could have, of course, created woman to always be fertile, but He did not. Why? What other loving reason is there other than the fact that God does not want a married couple to lose the unity of their marriage, or to fall to temptation, simply because they have a serious need to delay childbirth? Here is Pope Paul VI alluding to this in his prophetic passage in
Humanae Vitae:
That’s all wonderful and beautiful, but it has no basis in tradition or the fathers. Quite frankly it sounds like a quite elaborate attempt to justify a break with the fathers. Look at these quotes from this very website.
Clement of Alexandria
“Because of its divine institution for the propagation of man, the seed is not to be vainly ejaculated, nor is it to be damaged, nor is it to be wasted” (The Instructor of Children 2:10:91:2 [A.D. 191]).
How is intentionally waiting to have sex when you
know the woman is infertile not wasting seed?
Here is Clement again.
“To have coitus other than to procreate children is to do injury to nature” (ibid., 2:10:95:3).
The entire purpose of NFP is to “have coitus” and
not procreate.
Lactantius
“God gave us eyes not to see and desire pleasure, but to see acts to be performed for the needs of life; so too, the genital ’generating’] part of the body, as the name itself teaches, has been received by us for no other purpose than the generation of offspring” (ibid., 6:23:18)
Again, this rules out NFP entirely.
Jerome
“But I wonder why he [the heretic Jovinianus] set Judah and Tamar before us for an example, unless perchance even harlots give him pleasure; or Onan, who was slain because he grudged his brother seed. Does he imagine that we approve of any sexual intercourse except for the procreation of children?” (Against Jovinian 1:19 [A.D. 393]).
Is there really anything else to say?
Link
Now you can go on about “natural law” (speaking of natural law, most creatures in nature have sex
only when the female
is fertile, not the other way around

), and you can beg the question as to
why God designed us the way He did, and you can speak about the damage our contraceptive culture does; but in the end none of that comes from Apostolic Tradition.
If we are honest we have to admit that the Catholic Church has
changed its teaching on this subject in order to accommodate modern society, a fact that many traditionalist Catholics are more than happy to point out.
