I don't dispute that. But in most those 'other countries' literally anyone could be hiding a knife as easily as someone in US could be hiding a gun. So it appears in the vast majority of the cases where people are already right next to each other where both a knife or gun could kill someone, whether it is a knife or a gun is almost a moot point. It's only at a distance that you can treat a knife as a less lethal threat. Therefore the problem lies with the police, by vast majority.