In my experience, the worst people to have in the military are the ones who don't want to be there. They often don't participate fully, and are just dead weight to carry forward. At least, that's my Air Force experience... And those are the ones that joined willingly... Most air force leadership will let people out of their 2nd term of enlistment if they don't want to be there, because its better than trying to force someone to participate.
That's my 2 cents. Perhaps the Army handles people who don't want to be there better, but I'm not sure I would want to lead a bunch of people who would rather be somewhere else. Especially when it comes to matters of national defense. I think the military would rather not have conscripts or the draft for that very reason.