My point being, that if there were a situation in which the US needed a draft, the situation would probably be quite bleak. The time it would take to register everyone would add months, even before there was a draft itself. Why not just have everyone sign up when they're 18, and if the country is faced with such a dire emergency that we would need to draft our (obese and undisciplined) civilians then it could be done immediately?
In theory. Why not just keep a roll call before the crisis occurs?