The US prison system and the harsh police also contribute to violence, people are more violent because you are violent with them, it works as a feedback loop.
chicken and egg problem. I don't think US society was ever "not violent". It isn't more violent today than it was in the 80's at least.
Or consider Japan. They have a 99% conviction rate, and a big part of that is because it's an open secret that police will torture confessions out of people they arrest. But once again a different people with a different culture and we see an incredibly low crime rate.
For this matter we can perhaps even look at the US! Violent crime rates have been plummeting since the early 90s even though that has been paired with a sharp increase in the public perception of police violence. If there was a feedback loop then we would expect it to have been going sharply in the other direction!
Also, torturing people into confessions is a great idea, until you nab the wrong person. But it sure drives the conviction statistics up!
This isn't a question of culture, this is simply a case of the police fudging the numbers to make themselves look good. The Soviet Union also had "zero crime", and a 99% conviction rate, but unlike Japan, nobody took those bullshit claims seriously.
[1] https://www.washingtonpost.com/news/morning-mix/wp/2014/03/1...
But GGP realusername's claim was that brutal policing drives crime. Places which have brutal policing and genuinely low crime are some evidence against this, even if you don't wish to emulate the brutality.
(Whether the USSR had low levels of street crime I actually don't know -- is this known? But few deny that Japan and Singapore are pretty damn safe.)