Pinker is certainly much above the typical academic of today, but reading his arguments, I can't help but conclude that even an exceptional figure such as him is nowadays incapable of discussing matters like these sensibly. He simply lacks an adequate and broad enough knowledge of history and other relevant fields, as well as a reasonably unbiased view of the modern world, and ends up constructing arguments based on a naive and cartoonish view of both history and the present.
On the whole, Pinker is great when he sticks to topics where arguments based on particular solid scientific findings suffice, like for example in The Blank Slate. However, his attempts at grand theories such as these, where a sensible argument would require a very broad knowledge of a great many things that is not offered by today's elite education, as well as many insights into the modern world and modern history that go significantly beyond the cartoonish textbook accounts, strike me as painfully naive and misguided.
One one hand I agree (facially the claim about the Enlightenment fostering resistance to slavery is particularly bizarre, or at least lazy.) On the other hand there's frequently great value in works that painstakingly document an empirical trend, even if the causal explanations they offer inspire skepticism - the work of Gregory Clark comes to mind.
I wanted to bring attention to two posts from Razib Khan's Discover magazine gene expression blog (some of you may have been readers of the still active original gnxp) on the polemic surrounding Pinker's The Better Angels of Our Nature.
Relative Angels and absolute Demons (and the related But peace does reign! )
I generally agree with some of his arguments, but found this quote especially as summing up some of my own sentiments: