Ah, I see Pinker is trotting out Jonathan Haidt and moral dumbfounding again. Psychologists aren't usually very good philosophers and Pinker isn't any exception. His treatment of the philosophical issues involved in morality is quite shallow.
Unfortunately for Pinker, people tend to respond in the same manner to questions about scientific beliefs. They immediately declare that, for instance, the earth is round and grope to justify it. Most of them end up saying "I don't know, I can't explain it, I just know it." Some of the smarter ones might say that scientists have an explanation. A few might even be able to give a justification. Do a straw poll at work and see for yourself. I asked about thirty university educated friends (several with masters degrees in science and engineering) and one person managed to come up with "satellite pictures." None could even tell me that when a ship comes over the horizon you see the top of the mast first and then the mast, etc etc, let alone come up with a scientific or mathematical proof.
The fact that an area of the brain associated with emotions doesn't mean that emotion causes the judgment. It's most likely that people have been brought up at a young age to believe such things are wrong, and they feel a strong emotion because of this belief that the act is wrong! The belief causes the emotion, not the other way around.
If you want far better treatments of emotivist/expressivist theories of ethics I'd suggest you turn to Simon Blackburn or Alan Gibbard rather than Steven Pinker.