All of which is irrelevant if someone decides to break the law and murder someone. Do you think the truck rampage terrorists care about training, licenses and insurance LOL? Murder is illegal, the legal system in the US is far harsher than ours, it's no deterrent at all to criminals, nor would any gun regulation be. What is so difficult to understand here? What regulation would you suggest they could implement that would have any impact at all on homicides that they haven't already. 200 odd million legal gun owners and a fraction of a percentage who break the law with them, should we ban vehicles because some people drive without a license and insurance? PC culture doesn't allow America to get a grip on homicide rates in the same way as knife crime isn't addressed in London. People want to blame the government and strip every single freedom for everyone else rather than make criminals take personal responsibility, its pathetic.
You have also ignored that the states/cities with the toughest of gun laws (hows Chicago doing?), have pretty much the highest gun crime and homicide rates, so yeah that's really working well isn't it, who would have thought that criminals don't give a toss about regulations! Idiotic.