Islam has often been considered a Christian heresy and often been considered a Jewish heresy. Basically, it was a syncretist creation of its pagan founder, who revised it a couple of times with convenient visions when it wasn't getting him what he wanted (more booty). Islam is a cult, creating its own closed world with its own delirious and irrational standards, behaviors and society, just like the cult in California where all those nuts killed themselves after filling their pockets with quarters to call home from outer space.
But Islam was a cult that happened to come along at a time when the world was ripe for cults and there was no authority left in that geographical region strong enough to stifle it at birth. This is one of the very good reasons that the Church exercises authority in matters of faith. Had the Church stamped out Islam many centuries ago, it would have been to the benefit of us all. This shows the importance of objective truth and the value of authority.
Don't cults normally self implode after a few years?