You used to hear of judges who would tell a young troublemaker that he could either join the Army or go to jail. I doubt that happens much anymore.
In any modern military, more and more jobs are technical in nature, and it takes study and dedication to learn them. Having been an NCO, I really can't imagine trying to train subordinates who absolutely did not want to be there.
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"We are fast approaching the stage of the ultimate inversion: the stage where the government is free to do anything it pleases, while the citizens may act only by permission – which is the stage of the darkest periods of human history, the stage of rule by brute force." – Ayn Rand