In addressing the failure to date of the project to spread Western liberal values to the Middle East, Lee Harris doesn't argue as others have that the project is ill-conceived; merely that it is naive on two counts: it overestimates the potency and appeal of liberalism, and underestimates the effectiveness of Islamic fanaticism as an alternative cultural paradigm.
The problem is that we in the West have come to think that man's natural proclivities, if allowed, will tend towards reason, rationalism and enlightened self-interest, when in fact tribalism and the rule of the jungle might as easily be thought of as our "natural" state. Our delusion leaves us weakened in comparison to radical Islam, and no less than the future of Western civilisation as we know it is at risk.
Harris constructs his a priori arguments with a cold but subtle logic, and they deserve to be both heard and heeded. But he sidesteps so many real world complexities that thankfully you needn't be as scared as he intends you to be.