I see you never got a reply to your question. I am obviously biased in favour of Pinker, but my perception is that "liberal hack" (and other epithets) is a mindless insult that people throw at him when they don't like to uplifting message that he's communicating, but can't find anything logically or factually wrong with his arguments or his presentation of data.

The closest I saw someone trying to have a legitimate case of showing Pinker misrepresenting reality, was the criticism of this passage (also from "Enlightenment Now"):

What proportion of pairs of ethnic neighbors coexist without violence? The answer is, most of them: 95 percent of the neighbors in the former Soviet Union, 99 percent of those in Africa.

(i.e. only 1% is at war)

Critics pointed out that, at the time of Pinker's writing, the number of countries in Africa at war was X, and X divided by the number of all countries in Africa is much greater than the 1%, so clearly Pinker is lying. But firstly, the passage talks about ethnic neighbours, not countries, of which there is much more in Africa and the former Soviet Union, and secondly, there is almost always more neighbours than there is countries in any region. For example in Australia, there are 5 states, but 6 borders (pairs of neighbouring states), so if Queensland went to war with New South Wales, 60% of the states would be at peace, but 83% of pairs of neighbours would be at peace.

Edit: grammar