The short answer is that in the US, anything that isn't specifically prohibited is permitted, while in many locations it's the opposite, and anything that isn't specifically permitted is prohibited. It's a matter of philosophy, and each country decides its own philosophy. Brits shouldn't be questioning US laws, just as we shouldn't be questioning British laws. Things are the way they are here, and won't likely change anytime soon. We do have a constitution, which prohibits the federal government from exercising all the powers it might like, and many of us support that constitution. I've been relieved of my sworn duty to support and defend it, but I will still do so, as long as I have breath.