Wasalam dear brother and welcome. And no worries, your language is quite nice compared to mine.
You wrote: “You are essentially saying that everything not explicitly prohibited in the Qur'an, which has history that can in some chain of transmission be conceivably linked back to Abraham should be considered the Creed of Abraham, and thus divinely permissible.”
First, I did not say the above. Perhaps I need to restate:
First, I am basing my arguments on 16:116, according to which no one can forbid what is not explicitly forbidden by the book. Making something Halal/Haram pertains to God’s prerogative. Perhaps, messengers can do so as well in certain limited circumstances, yet God asked prophet as to why he declared something halal as haram on himself. Since no verse in Quran prohibits circumcision, no one else can prohibit it using Quran and God. People can prohibit for some other reasons, such as medical, or esthetic, whatever, but not using the book.
“Chain of transmission” as mentioned by you is not really a historical evidence. To understand what is meant by “overwhelming historical evidence” as mentioned in my post one needs to understand the term “Millat.” Quran is not revealed today. It was revealed 1400 years ago in a language to a people who knew very clearly what various terms and terminologies meant in their language. If they were confused about any aspect of Quran, they asked questions and God responded as needed. We don’t find anyone asking a question related to the “Millat of Ibrahim”, when the command came to follow this Millat. It is thus abundantly clear, this term and its associated practices were well-known and practiced at the time.
The term itself in language means “Religion - a belief system, and practices associated with such a belief system.” See Lughat or Lane. Thus, not only people knew the Ibrahimic practices, they practiced those as well. Prophet Muhammad himself was well-aware of those practices as do other people of the region, and he must have participated in some if not all of those practices as well. The prophet’s own tribe Quraish was caretaker of the House built by Ibrahim. Thus, they must have known and practiced whatever practices were associated with this House too. So on and so forth. These are just logical conclusions. The religion however degenerated, particularly the belief system, and adopted polytheistic underpinnings. This is clearly referred to and corrected in Quran, when it says “Ibrahim was not a mushrik, etc.” at various places.
With respect to circumcision, you find not only Arabs, Christians and Jews were practicing it too. This itself is such an overwhelming evidence that it does not need any “chain of transmission.” You can ask any Muslim family (Shia, Sunni, whatever) today, do you do this practice? What will be there response? In fact, no Muslim needs to ask about circumcision being practiced or not, rather every male (except perhaps new converts) is living through this reality. Assume, if today a book is revealed and ask Muslims to follow the Creed of Muhammad. Will circumcision be part of it or not? The answer is obvious.
The above was to establish that “Millat Ibrahim” was well understood concept and practice at the time, hence, requiring no “chain of transmission”. Quran provided corrections and prohibitions wherever needed. Since it did not provide any correction and prohibition, it is understood to be sanctioned implicitly. This is not an isolated case related to Ibrahimic practices. One can think of other such practices as well, some mentioned in Quran and others not. These practices are now also called “Sunnah” and linked to Prophet Muhammad since he purified and sanctioned them.
Now to your this claim: “… But the moment you suggest that circumcision is indirectly, but divinely prescribed by the Qur'an because it reflects what took place during the time of Abraham, and is thus falls under the "Creed of Abraham", this argument falls apart looking quite unpleasant. Unpleasant because such an argument could be applied to essentially any and all retro-grade practices of old that have history that can supposedly be linked to Abraham but aren't explicitly mentioned in the Qur'an, conferring upon them all a divine support from the Qur'an no-less.”
First, I did not say, it is “prescribed” by the Quran. When Quran prescribes something, it becomes mandatory. I stated it gets “implicit sanction” by the Quran, and it is indeed one of the Ibrahimic practices, sanctioned by the prophet himself, else it could have never been universally practiced by Muslims East to West, North to South as well as other Ibrahimic religions.
Second, my argument CANNOT be applied to “essentially any and all retro-grade practices of old that have history”. Creed of Ibrahim is a well-known concept and its practices are not only well-known, these are practiced as well. If you think my argument can be applied to “retro-grade practices” related to Creed of Ibrahim, please bring one such example.