They don't have the easy access to guns that we don't want to get rid of in the US. I've asked a few people this question: "If it could be so that you were allowed to kill anyone, anywhere. Nobody will stop you. You will face no legal consequences. You just have to produce a list of no fewer than five people you would definitely kill. Can you do that in the five minutes starting now?" You'd be amazed by how many answers I have gotten in the affirmative.
I want to believe that most people don't commit violent crimes because doing so is against their moral fabric. That is not true in the world (or at least the country) we live in.
But most criminals, even most murders aren't out of reach.
Note: I'm not proposing that there need not be control initially. Merely that we need to be better at giving up control over time. And yes, you'll find exceptions.
I think the main problem is 1. most people just don't care about anything other than themselves and 2. they don't see of themselves in the same shoes as convicts
The US have political problems. They are unfixable as long as most of you have given up.
Even the most invasive surveillance system is more humane that the US prison system.