Really I think all civilians victims in the last 100 years beg to differ. We might not have had another massive world war in the last 69 years but there's been plenty of bloodletting and human savagery. Nothing to show that under the right circumstances humans don't fall back to basic tribal violence.
I find the medical experiments performed by Japanese and german doctors during ww2 to be more frightening because they where done in the name of medical science by "modern" humans completely capable of emphasizing with their victims.
The great lesson of the Nazis and the Milgram experiments is that all/most humans are capable of great evil when it is socially normalized.
To think that humans do these things out of hate and dehumanization puts the cart before the horse. Rather, there are cultural drives that incentivize certain behaviors, leading people then suppress and rationalize away their empathy in order to engage in those behaviors and reap the direct or indirect social benefits.
The most common pattern is devastatingly simple: hating an out-group is a powerful way to create an in-group bond.
Erm ,what about the videos where people have been beheaded? I have not and will not ever watch one, but its not some tidy guillotine. What about Lee Rigby, the soldier in England who was run over, then hacked to death in a London street? The murderers who did that certainly would have no problem with killing people in cruel ways, especially if they were given state sanction.
For other morbid Medieval executions, read about being broken on the wheel. It's hideous.
