The law in the United States is that police must have some idea that you are committing a crime in order to stop and question you. This is called "reasonable suspicion" and it must be based upon some specific set of facts that a person would reasonably believe to be an indication that the person being stopped is breaking the law.
In this case, the police would be stopping someone that they believe ISN'T breaking the law. This stop would then result in the police being able to stop anyone at anytime, for no reason at all. Of course, if a person is then found to be breaking the law, they can be searched and arrested. These stops would soon be used as a method for police to stop and detain people who the police would like to find reasons to arrest, and allow the police to go on a fishing expedition.
I am glad the idea was scrapped here, but there are other places where the policy continues.