The Consequence of Treating All Ignorant Polytheists Equally
As previously mentioned, a misinterpretation of the testimony of faith must inevitably lead to further erroneous consequences.
This was also demonstrated earlier with an example when discussing the religion of Ibrahim (millatu Ibrahim). The pre-Islamic Arab idolaters considered themselves to be part of the din of Ibrahim عليه السلام and were even convinced that they held a particularly high status with Allah سبحانه وتعالى because they were the guardians of the ka'bah, the house built by Ibrahim عليه السلام.
Those idolaters also believed in the existence of Allah, worshiped Him, and even performed some of their ritual acts ('ibadat) solely for Him. They thus affirmed the general Islam and considered themselves to be upon the din of Ibrahim عليه السلام. However, despite all of this, they were not considered Muslims by consensus.
Therefore, whoever considers a polytheist to be a Muslim merely because he professes the specific Islam of Muhammad صلى الله عليه وسلم cannot avoid also calling those earlier polytheists Muslims as well.
The polytheists of that time would have had even more reason to be considered Muslims, as ignorance was far more widespread among them than in the period after the sending of the Prophet صلى الله عليه وسلم up to the present day.
After all, at that time, there was no complete and unaltered book from Ibrahim عليه السلام, like the Qur'an today. The people of that era, if anything, only knew remnants of the religion of Ibrahim عليه السلام, without even possessing a single written verse from that prophet.