AOA Dawood bhai, sorry for jumping in, it's been a while. Generally, I'd be one of the first to support your argument that a millennium of history can't be overturned on a whim and would require extensive evidence or otherwise very strong arguments.
That said, this argument of yours is logically very weak and moreover dangerous:
"You know very well that all is permissible except what is explicitly forbidden in the Book. Now I ask you where is the verse explicitly forbidding circumcision? None, whatsoever. If it is not in the Book, how do you come up with the notion they are doing something wrong? On the other hand, there is overwhelming historical evidence suggesting it to be one of the Ibrahimic practices. As is clear from other verses that Muslims are required to follow the Creed of Ibrahim, thus, one can understand why Muslims are doing it. Thus, all your inferences in this respect are untenable?"
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.
This is absurd.
This has nothing to do with religion or linguistics or semantics, but plain simple logic. If you can't see just how absurd and dangerous this argument is, then please consider it afresh.
And to be clear, if you were simply arguing that there is nothing in the Qur'an explicitly prohibiting circumcision so there is nothing wrong in having a circumcision done, I would mostly agree with you (except that for me this opens it up to debate on whether its existence as a tradition causes more harm than benefit to society; a non-religious debate). 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.
And please pardon my blunt language, but it reflects just how dangerous I found this argument.