Florida has a case before its supreme court, basically on open carry. The background is a man was convicted for failing to keep his weapon concealed. It was concealed poorly the very first time he lawfully carried a concealed weapon and became exposed to public view.
This YouTube video shows the State's argument against open carry and some pretty good questions from the panel of justices. You can see their reasoning and the rather lame reason's open carry should be illegal the State's attorney gives.
Remember, open carry and concealed carry each have their own unique advantages and disadvantages and neither method is superior to the other.
Oh, and the whole Second Amendment is pretty unambiguous: "A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed."