My counterpoint is that while "people are people", they are impacted and influenced by their material, cultural, and political circumstances.
People can become hardened, callous, mean, and damaged to a greater or lesser degree in durable ways that outlast political circumstance.
If you beat and abuse a child, and that child will be more likely to beat and abuse others. This is called the cycle of violence. You can absolutely have times and places where this is more or less prevalent.
"people are people" on a slave plantation as well, but their behavior is not the same as those living in Seattle. If you flipped a switch on the political system overnight, the people would not flip with it. You might expect to see trauma and damage to impact behavior for generations to come, even if you magically teleported them to Seattle.
I know families that fled the cultural revolution in China, and it still has behavioral impacts on people 60 years later, including children who have never even been to China. Many viewed their neighbors as threats, thieves, and informants and are less "nice" to strangers as a result. It changed who they are as people in durable ways that outlasted the causal circumstance, and informed how they teach their children to treat strangers living in Seattle 60 years later.
Surely you can imagine a place where conditions are not conducive to "being nice" and as a result, people are less nice overall. You might see the same absolute range, with examples of extreme kindness or terrible behavior, but the mean and typical behavior can be shifted.