If you are setting out with the belief that the physical world is reality, and especially if you believe God made it, then that background acts as a 'context' in which you read all of the rest of the Course. There is so much in the course written about undoing false perceptions and becoming able to see the real world or forgiven world etc, that it's possible to read into that to mean the physical world is reality.
For example, the course does say things like.... you must undo your false perceptions.... your false perceptions are clouding your perception of reality.... once you undo false perceptions you will see clearly.... then you'll see you brother as Christ and will see the beautiful forgiven/real world.... etc.... and there isn't specifically anything in those 'pieces' of the Course - if taken out of its total context - to challenge the notion that the physical world is real. So that can lead you to believe that this fundamental idea that the world exists goes unchallenged by the Course.
Another example is that people heavily believe they are bodies. They read things about how they should just accept the world 'as it is' and change their mind, and this leads to this kind of 'separation' between the mind and body. i.e., that we should let the body do whatever because its not real (a level confusion) and we should let the world do whatever because it's not real (a level confusion). And that's really a kind of paralysis, and a lack of responsibility, and a total lack of power (especially over death, which is a key part of the Course).
It is very possible therefore to take most of the course and slot it into an existing belief system and have it seem to mostly make sense. So then in order to bring the truth into the world, instead of bringing the world to the truth (in which it dissolves), people will try to sort of 'glue together' the broken pieces of out-of-context metaphysics, such as to say God made the world, the world is heaven on earth, the body can live forever, God made beautiful stuff in the world and sustains it, etc... none of that is in the course, but those finer points are easy to gloss over and ignore.
As I go back through the ACIM text and read it slowly and really digest it and ask myself what it is saying, how is it consistent, I continually see evidence that it is quite literally saying "there is no world" and that heaven and the world are completely opposed, that God did not create it - we did, that the world is something we 'made' as an attack on God, etc. Its not just our perception OF the attack that is an attack on God. The world ITSELF is fundamentally an attack on God, down to the very fabric of spacetime.
And on the point about perception, it is CLEAR in the text that the only point of having true perception (right mindedness) is that it parallels the One mind and allows us to transition to the one mind, which exists entirely beyond the world. Everything Jesus says clearly indicates this physical world is an ILLUSION and a dream and is not reality and never will be reality. It is VERY difficult for us ego humans to accept this as truth, and that is why the ego is extremely careful to disguise the evidence of this and gloss over the truth.
I guess I'm making this point because I continue to see prominent people 'teaching' other students with statements that seem to exalt the world and make it seem spiritual, but which is in fact the complete OPPOSITE of what the Course is actually teaching. As clearly defined in the Disappearance of the Universe, for example, which IS aligned with the Course's message, the world is basically a giant turd, metaphorically speaking, it holds nothing that we want, it is not our home, it is nothing more than a nightmare or bad dream, and IT WILL DISAPPEAR because it is not eternal.
It is quite a severe distortion of the Course's message when, within the wrong context, it can seem to be saying that the world will transform into heaven or the the world is God's 'movement' or that bodies are a permanent form of identification etc. The idea that the world is exalted and filled with any kind of truth is the absolute opposite of what the Course says and a total misinterpretation of its meaning. Imagine you believe an interpretation of truth that is 100% false. That's what many people are doing. To believe the world is our spiritual home is an absolute farce, and is precisely how the ego wants to INTERFERE with the Course and absolutely distort it to its aims of KEEPING ITSELF GOING.
The world isn't real.