We can reduce a lot of what the Course teaches seemingly down to simple statements such as "god is". But then when you try to extrapolate that back out to properly describe what we're experiencing, it doesn't work. Information has been lost. "God is oneness" or "there is no separation" is WAAAY too vague as a starting point.
If "God is", then when we try to explain what's happening in this world, or why I was woken up this morning at 7:30 by an alarm clock made of plastic and metal with electricity running through it, the "God is" teaching simply does not cut it. If we rely just on that, it's going to mean, God is an alarm clock.
All manner of false conclusions come from OVER SIMPLIFYING the metaphysics. This simplification is too basic to BASE an entire thought system on, or to structure an entire set of metaphysics on. It's all very well going one direction to make things more simple, but when we then turn around and use that simplified version to draw conclusions, it's just too basic. You won't end up with the same conclusions.
"God is" is an extremely high-level aspect of the truth, and conclusions drawn from these super-simplified ideas can be very much in error. God is not the one dreaming, and God did not create death or this world, which would be natural conclusions drawn from this. It's not accurate enough.
This is also why ideas of oneness and nonduality are severely prone to all kinds of false conclusions which STEM FROM the overly basic nature of these concepts. They simply do not properly or accurately describe God's nature and lead to so many "implications" that are false, that basing all kinds of conclusions on "there is only God" or "there is no self" or "there is one self" etc simply produces a huge amount of error.
The truth is supposed to be simple. But in terms of conceptualizing it, it's not simple, and without enough accuracy in the definition or what reality is or is not like, we just are going to find ourselves confused and mistaken. This is partly why the Course itself is SO HUGE and detailed, because there are so many nuances that CANNOT Be properly communicated using such simple terms. It's unfortunate but concepts, being of the ego, can become much more complex the closer you get to the truth, if you want them to be accurate. "God is" is nice, but it's too basic.
This overly basic reduction of the Course and the false conclusions which come from it, has unfortunately HAPPENED, and a huge percentage of the ACIM community has been somewhat misled into false teachings and false conclusions based on massively over-simplified concepts. There are countless statements in Jesus's words to demonstrate this.
As a result, we now have concepts of non-duality and having no self and the idea that the sonship is of the ego and that there are no souls and that there is only one person responsible for the dream and that you are responsible for other people's choices and so on, which are all false, which result from STARTING AT a way too basic concept or starting point.
Great teachers and poor teachers alike have fallen into this trap in a big way. There is huge portions of Jesus's teachings which have been misrepresented. Particularly in the areas of identity/responsibility, the performing of miracles, and overcoming death. The "natural conclusions" drawn from faulty logic has basically glossed over significant major teachings, and has turned A Course in Miracles into a sanitary and watered-down way to fix yourself and get out of here.
This is a Course in performing miracles, becoming very powerfully minded, reversing literal death, and being one of many sons of God who temporarily demonstrates perfect health in the dream while teaching and helping all brothers to wake up through miraculous demonstration.
This message has been largely destroyed by well-meaning but misguided teachings and poor reasoning. We need to almost start over with a much more accurate and all-encompassing view of the Course which does not omit things Jesus said, does not see contradictions where there are none, does not turn a blind eye to things that don't seem to make sense, and does not filter OUT the very heart and soul of the Course itself.