Those spring-loaded pocket knives open faster than a butterfly knife, so why are those legal and butterfly knives are illegal? I have a dull butterfly knife that I use to practice, but I don't understand why I'm not allowed to buy a real one. Yet my friends carry spring-loaded pocket knives that they can flick open in a fraction of a second. I don't get it.

What are the United States Laws in regards to situations like this? Is it legal for people to carry weapons such as swords and other dangerous weapons on their persons in public? Technically they are not concealed and after doing a brief google search, there was nothing on the subject. Does anyone have any more knowledge?