This is Ba Sing Se levels of delusion for some people.
In fact, there are plenty of commentators downthread who don't see it as a mistake either. Years of demonisation and propaganda has gone into supporting the belief that as soon as somebody steps out of line it's necessary to beat them back into line, or shoot them if they do not comply. It's no more a mistake than the millions of people in US prisons: it's policy.
US police forces seem to have a very short training which, as far as I understand is not centrally vetted by any federal organism? And considering the short training time it seems to be mostly focused on tactical and firearm training.
Compare that with European forces and you see a completely different reality. In Europe the police is generally seen as peace-keepers, force is absolutely a last resort (probably not so true for crowd control units but certainly true for daily policing).