Of the two boldface sentences in the OP, the first represents the book rather accurately, while the second does not.
With regard to the sentence "It argued that Muslims are driven to violent actions by their violent religion".
The book says
The speciousness of this claim [Islam is no more amenable to violence than any other religion] is best glimpsed by the bright light of bomb blasts
In his own press release for the book, on his own website, Harris has written:
excuse religion as the basis for violence, preferring to maintain, against all contrary
evidence, that only economic and political motives fuel extreme violence.
With regard to the second boldface sentence "Even moderate Muslims harbour dangerous and savage thoughts that make them an enemy within":
According to the New York Times review of the book:
Harris reserves particular ire for religious moderates, those who "have taken the apparent high road of pluralism, asserting the equal validity of all faiths" and who "imagine that the path to peace will be paved once each of us has learned to respect the unjustified beliefs of others." Religious moderates, he argues, are the ones who thwart all efforts to criticize religious literalism. By preaching tolerance, they become intolerant of any rational discussion of religion and "betray faith and reason equally."
However, Harris has also written a separate article Who Are the Moderate Muslims?. There he praises Abdel Rahman al-Rashed as a moderate Muslim.
In fact, the book actually says:
This transformation, to be palatable to Muslims, must appear to come from Muslims themselves. It does not seem much of an exaggeration to say that the fate of civilization lies largely in the hands of "moderate” Muslims.
So he is casting moderate Muslims in almost a heroic role, certainly not the enemy within.