Violence might not be the exact opposite of peace. Intuitively, peace seem to mean a state where people are intentionally not committing violence and not just accidentally. A prison might have lower violence than an certain neighbourhood but it might still not be considered a more peaceful place exactly because the individual proclivity to violence is higher despite the fact violence itself isn't. Proclivity matters.

I am generally sceptic of Pinker. I have read a ton of papers and Handbooks of Evolutionary Psychology, and it is clear that while he was one of the top researchers in this area in the 90's this has dramatically changed. The area has shifted towards more empirical precision and fined-grained theories while some of his theories seems to warrant the "just-so story" criticism.