Should Revenge Have Bounds?

I recently finished Steven Pinker's book attempting to explain the decline of human-on-human violence over the last twenty thousand years. All in all, I recommend it. It has noteworthy psychology nuggets on nearly every page, explained with good data and lucid metaphors. I especially enjoyed how he built up many cute explanations of various phenomena--like the Freakonomics-popularized abortion theory of the crime rate decrease in the 1990s--only to soundly and evenly debunk them. My two major points of disagreement:

1) As Tyler Cowen argues, it is possible that although the mean number of causalities from interstate conflicts has been falling, the variance has been increasing. Aside from WWII, we can't easily observe this variance, though we can see signs of it in events like the Cuban Missile Crisis. Pinker employs per-capita log-scales for many of his charts and on these WWII does not seem quite as bad, but still it sticks out indelibly.

Wisely, Pinker does not project the decrease in violence indefinitely into the future, rather seeking to explain what we have observed so far, so his thesis is technically immune to this critique. Still, I imagine that there have been some not-easily observed historical aberrations which, if they had gone differently, would have meant that this book would never had been written. The winner's curse comes to mind.

2) As one reads about the incredible violence that occurs in US prisons, it is difficult not to wonder whether the benefits to decreasing violence always outweigh the costs. I have previously written about the protection vs freedom trade-off. The laudable decrease in person-to-person violence comes at the cost of constraining the actions of individuals by probabilistically putting them in prison. This is an imperfect process and has negative externalities in that it further exacerbates the burden of those locked up for non-violent crimes.

So, I would have liked to see more discussion about the violence in modern-day prisons and whether it is more apt to say that violence has been displaced rather than decreased. In a provocative article, Christopher Glazek argues that the US should be more like the UK and have slightly looser violent crime convictions which would make the conditions in prison slightly less awful. In most cases I would probably come down in favor of protecting innocent bystanders, but it is a conversation that needs to happen and that I wish Pinker had addressed.