A car weighs at least ten times as much as a go-kart, child. That affects how long it takes to stop and how much damage it causes in a crash. Cars are much more dangerous than go-karts and even if you drive perfectly well other people on the road may not. Driving schools can teach you defensive driving so you know how to react when you realise someone is going to crash into you. There are a lot of regulations in America and some of them seem entirely pointless, but those around driving are very much not.