If your state isn't red, you do. If it's green you need a license first, if it's light tan, you don't. Dark tan has no explicit law and have never outlawed it, so federal law takes precedence, which allows open carry. Of the red states, most of the ones in the South have the law on the books from the Civil War, and have just never bothered to repeal it.
Now why is it people are freaking out and demanding people should be arrested for following the law in those 43 states? Is it, perhaps, that this lack of exposure to a piece of machinery is what fosters so much fear among people?