There's a side to the Koran that's not so dark. That's what Cat Steven's draws from. But the violent verses of the Koran have more scriptural support because they came later and supersede the gentle verses. It's a schizophrenic religion same as it's founder.
Having read it in its entirety, it's a small side, and it lives in the shadow of the other. As for Cat Stevens, he's an idiot.
The biggest problem with Islam is that the religion depends too much on the Imams to "interpret" the meaning of the Koran for its followers (though it is quite clear in most cases). If an Imam decides to preach one side or other of the Koran, then that's what the religion is for that group of followers.
In the end, however, the goal of the Koran and all of it's followers is to see the entire world under Islamic rule. And the Koran is quite clear about how to go about achieving that goal. It's called Jihad. War.
Christianity also seeks to convert the world. But the Bible does not advocate war as the method. Nor does any other major religion that I am aware of.