This is an interesting article. The author compares ACIM with Book of Urantia. I know very little about Book of Urantia.  Some things have made me skepticle of its validity. Nevertheless, it is interesting to see how two sources that are supposed to be channeled oppose each other.

I believe the author of this article makes a lot of good points. He says the below:

"Because all these doctrines are irreconcilable with the UB on such fundamental issues, it is clear there is no way to harmonize it with ACIM.  ACIM takes an absolutist position.  It purports to be the unqualified, absolute truth.  It denies all relativity.  Its view of reality is black and white: pure black and pure white.  If you disagree with its teachings in any way, you are ipso facto wrong, insane, and lost in your ego.  You either know everything (literally), including the truth of ACIM, or you know nothing (literally).  Therefore, it is impossible to take a moderate and modulated position towards ACIM; ACIM forces the reader to respond to it in absolute terms.  If you think you can pick and choose what you like and don't like about ACIM, then you don't understand its message and you are not taking it in the serious terms it demands of its readers.  This is how, I believe, some readers of the UB manage to find a "compromise" between the teachings of the UB and those of ACIM.  They are philosophically naive, complacent and lazy.

If you disagree with ACIM-and I disagree with it fundamentally-or even if you disagree with it partially, then you are forced, by the terms of the book itself, to decide whether you or the author is insane.  That is the challenge that ACIM hurls at you.  Can a conscious son of God disagree with ACIM?  ACIM makes this is absolutely impossible.  I declare that I am a conscious son of God, and I say that ACIM is entirely rubbish.  Since the author of ACIM must respond by declaring me to be insane, I have to reply by declaring that the author of ACIM is the one who is insane.  There can be no compromise."

http://www.freeurantia.org/acim.htm