But they don’t honor the God of Abraham; they reject the Old and New Testaments. They reject the old by claiming that Ishmael, not Isaac, was to be sacrificed by Abraham. They reject the new in that they say Jesus was only a man.
Having been given the Scriptures, how can they be seen as honoring the same God? Their Koran is in direct contrast with the Scriptures.
What’s more, I believe (though I am no scholar, and will yield if I’m wrong) that Allah is capricious and not bound by either free will or natural law. This is a key difference between the Judo-Christian. Jesus showed God as a loving Father, who we could come to know through his creation. Islam means ‘submission’.
And that would be my point. Do you say its another god, or say they aren't honoring God? There is a valid argument either way, but I prefer the latter, because it doesn't confuse the subject.