But I'm not failing to acknowledge that. I asked for definitions of denominations.
You always fail to acknowledge it. "Islam is a totalitarian ideology", "Muslims think peace requires global conquest". You've repeatedly argued that there is no need to qualify your statements when talking about 'Islam' and 'Muslims', and always interpret the Wahabbi types as being the most representative example of what Muslims should believe.
What definitions of denominations do you want? What would it tell you? If you knew that most Yemeni Muslims were (nominally) Shafi'i and most Indonesian Muslims were Shafi'i how would your understanding of the situation be improved? 'Indonesian Muslim' gives you more information than 'Sunni of the Shafi'i madhab'.
There aren't any nice little tags that you can point to to show which are 'good Muslims' and which are 'bad Muslims'. Even a term like Salafi is very problematic as there is a part of the Salafi movement that is completely apolitical and part that is violently political..
That said, there must be some essential aspects of Islam that are close enough to being universal that we can - in fact - make some general statements.
Yes, but that doesn't mean we can make any generalised statement we want.
There is one God, Muhammad is the messenger of God, the Quran was revealed to Muhammad by God. That would cover almost all Muslims. They should fast during Ramadan, give to charity, pray towards Mecca, etc.
So, what next? Religious texts are vague enough that they can be interpreted in multiple ways, that's why religions survive so long. They are adaptable.
You get a better understanding of what a religion is by looking at society than looking at texts.
Christians believe Jesus was a good chap with a strong moral message, but what do an Syriac Orthodox Christian and a German Lutherian have in common? On average, do you know more by knowing someone's nationality or knowing their Christian denomination?
Of course religion has played a role in the development of culture, but it was only one factor out of many. And religious influence is only in part related to the scripture of the religion, and part influenced by other human factors.
I have to say this argument of yours also seems weak because Muslims are often heard to complain that a certain action offends all 1.6 billion of them. So which is it? Do Muslims have some things in common or not?
When Jessie Jackson speaks on TV do you assume that his views represent all black people, everywhere?
Anyway, I don't get where your reasoning is going. There is an enormous leap between "all Muslims have a few symbolic things in common", and "for Muslims the word peace means only after they have finished their global conquest".