I think it's a bad idea. Personally, from the military perspective, I don't want to rely on someone who doesn't want to be there. There's enough screw-ups in the ranks as it is, this would just make it worse.
On a side note, even though I do not agree with a draft, I do think everyone should serve. I know, kind of contradictory, but hear me out. A draft would only be used in time of war. That's when you get all the wonderful anti-military people coming out of the woodwork. But if the country made it mandatory to serve 2 years in any branch of the armed forces, we would:
A: Have a bigger pool of people to go to war with if need be
B: Kids would have a better understanding of what the military is all about
C: Kids that aren't going to college would get trained in a skill they can use on the outside
D: Discipline, that's all!!
And I truly believe that if we made everyone serve it would greatly reduce the number of anti-military types, if for no other reason than the fact that people are less likely to bash something they were once a part of.
Think of it this way, you're 18, just graduated, with no desire to go to college. Unless you went to a vocational school, your job choices are limited. But, if you went in the service, they would teach you a job. In my case, aircraft maintenance. So you could be a crew chief like me, on any plane in the inventory! At 18 you would have your name painted on the side of YOUR plane! Considering the cheapest birds we have right now are around $30 million, that's a pretty big honor to bestow on a teenager. If turning wrenches isn't your thing, there are literally hundreds of jobs to choose from. Anywhere from medical, to human resources, to aircrew, to financial consultants, to payroll auditors, you name it, the military has it! They pay you to learn, give you college credits for every class you take for your job, give you money for college, and give you the all-important job experience. Really not a bad deal if you look at it!