The left is rudderless so they will be looking for many an avenue to establish some kind of relevancy; it wise for those on the right to follow these intellectual trial balloons.
Warraq's point is that Islam has gotten a pass on criticism in the West for various reasons (buy the book for details) and a pass in Islamic countries because, well, the critic will be executed.
As a Christian I look at Warraq's book as a resource about Islam from a Muslim who had taken a closer look at the faith and sees that it does indeed have some problems and there need to be answers. I also place Warraq in the same camp as the disaffected Christian writing a book on the abuses of denomination "X".
The Bible has already gone through numerous cycles of textual criticism over the past couple hundred years and has weathered the critiques pretty well. The Qur'an has yet to go through that process, and that is Warraq's point.
For those who don't want to purchase the book but would still like more information about Christianity and Islam, take a look at Answering Islam.