Answer:
When you are accused of a crime, the law does not immediately treat you as being guilty. But, after you're properly found guilty under the law, you are treated differently-- you lose rights, you are punished, etc. The key to the American system of justice is that everyone is treated the same until that legal decision is made as to guilt or innocence. It has to be that way in order for the system to work. Since the law does not require anyone to prove their own innocence, they have to be presumed innocent until and unless they are found guilty by the proper process. If you take a few minutes to imagine how it would work the other way around, you'll immediately see the wisdom of this system.