The problem isn't the Koran, which is considered the "Holy Word" equivalent to the Bible. The problem are the hadith, which are the alleged sayings of Mohammed, but without the care and scholarship of the Koran. Many moslems question their authenticity, and they don't have the same stature as the Koran. It is some of the hadith which can be said to advocate violence, but acceptance of the hadith is far from universal among moslems. In fact, it's the varying acceptance of the hadith that leads to many of the schisms we see in the islamic world. But the Koran does not advocate the killing of nonbelievers, and so all of islam isn't tainted. A bit like some of the whacked-out radical Christian sects that tarnish our own history.
Study the crusades a bit. The moslems treated Christians and Jews far better than the Christians treated either jews or moslems. The real author of radical islamic fundamentalism was the Egyptian writer and activist Sayyid Qutb, who was executed by the Egyptian authorities in the mid-1960's for inciting resistance to the regime. But that guy didn't even exist until the 20th century, and Islam has a far, far older history than that. It's not the religion -- it is certain practioners of and sects within that religion that are the problem.
The bottom line is that people who claim that islam is an evil, violent religion are only revealing their own ignorance and lack of historical knowledge.
Really? What does it say about Christians who convert from Islam?