Let me cut the Humanae Vitae quote down to smaller size:
The Church is the first to praise and commend the application of human intelligence to an activity in which a rational creature such as man is so closely associated with his Creator. But she affirms that this must be done within the limits of the order of reality established by God. Paul VI, Humanae Vitae
First of all, you’re taking the term “natural law”, which has a specific theological history and meaning, and deciding that it means no more than what you personally attribute to the individual meanings of the words “natural” and “law”. Your first clue should have been the word “law”.
There are two kinds of law: those that enforce themselves and those which require a judge. There is no subset of the law in which those being judged get to decide for themselves what the law says. The case you are making has been made to those who have the authority to decide what it is that moral law says. It has been decided in terms you don’t like, but as many a lawyer will tell you, it does no good to keep arguing the point after the case has been decided.
If you want to know how it is that ABC defies moral law and proper use of NFP does not (because there are ways to misuse NFP in order to reach selfish ends), then there is Humanae Vitae, there is Theology of the Body, and there are many scholarly commentaries on those two that exist to answer your questions. If, instead of getting your honest intellectual questions answered, you want to argue the point that these explanations of moral law are wrong and you are right, such that the Church teaching on this point should be overturned by some sort of juridical avenue or popular vote, then you are beating a very dead horse.
If you won’t believe the Popes, you aren’t going to believe us.
I’m using the traditional definition of Natural law, dating back through Summa Theologica to Aristotle. There is a reason why philosophers and theologians gave up arguments based on Natural Law - the arguments don’t work. They don’t work for several reasons: one is that the duality of mind/body as pictured is not really correct - i.e. we are not separate from nature in the way that was assumed and so an argument based on the concept that we should not interfere with what is natural doesn’t make sense. Another argument is that it is generally the case that natural processes serve multiple functions simultaneously, and often what appears to be the most apparent function very often is not.
Are you arguing that we can, in fact, determine which process God intended as primary, and that we would always be right? And what happens, as has happened here, that our observations of the world change, calling into question our initial assumptions?
I am not inventing these faults with Natural Law arguments - the faults were discovered by men smarter than me long before me. That an argument was based on Natural Law initially is frankly an error to begin with.
In the instances where a case has been decided, but the logic used in the case was incorrect, it often does good to continue to raise the case and similar cases, so that the Court gets another bite at the apple, and eventually can get it correct.
This isn’t to say that there aren’t fundamental beliefs which Aristotle and Thomas attributed to Natural Law/Natural Justice - much in the same sense as Cicero did.
Yet, fundamentally, the concept of natural law is as mistaken as the Newtonian concept of an objective universe, separate from ourselves. We know only what we observe, such a separate universe (and consequently separate Natural Law derived from such a universe) cannot be known. Today we know that the observer is in fact part of the observation. (Heisenberg, Polyani)
We do not reveal God. God reveals Himself.
I will read again the pieces you suggest. However, to this point, they are unconvincing for the reasons previously stated. Eventually, this untenable position will change, not because of a vote - but because it is right.