What is it here that you disagree with?
I don't think we do disagree on fundamentals. Rather we have different perspectives on what "Islam" means. To you Islam means the collective views of billions of Muslims over many centuries (including Abbasids, Ottomans, Sufis, Shias, etc. and modern day Muslims) So if you are going to take into consideration the beliefs of all those billions of people, of course there will be many interpretations. To me, Islam means what Muhammad wanted Islam to be during his lifetime alone based on my own study and interpretation of the earliest sources of his life, it is largely irrelevant to me what some 12th Century Sufi poet wrote, or how some Abbasid Caliph treated minorities.
One single book: Ibn ishaq, is pretty much enough to read to get a good idea of what Muhammad himself wanted Islam to be about. That is the oldest source after all. Those hadith collections that Sunnis use (Bukhari, etc.) are also useful as a back-up, but they don't contradict Ibn Ishaq, they paint the same picture in fact.
Are you saying that IS represents the only true form of Islam?
I am looking through my posts in this thread, and I honestly cannot find anything I wrote that would have given you that idea. Let me repost what I said yesterday:
But let me stress that I never meant to imply that they are the only group that do not contradict Islamic principles. I think that even the original Islam was probably broad enough to include a variety of philosophical outlooks and lifestyles. That is why it was a success.
The original Islam appealed to warriors who wanted war booty and slave girls. But it also appealed to peaceful poor folk who wanted to benefit from Zakat, it also appealed to slaves who saw conversion as a chance to escape their misery, it also appealed to people longing for "spirituality" and felt like there must be more to life than meets the eye, etc. Most of those people are still attracted to Islam today, and not all of them are ISIS thugs.