There are those who believe that they have an argument that justifies military conscription in certain circumstances. That argument is that conscription is justified when destruction is eminent. (The below does not depend on my portrayal of this argument.)
What I would like to present is an argument against even this limited justification of military conscription. Take the situation where military conscription is supposedly justified, ie. when destruction is eminent. Say that at this point some try to use force to get others to fight with them (military conscription), justifying it with the argument above. Then say that those who are being conscripted refuse to submit. This refusal could lead either to some form of imprisonment, either now or after the conflict, or to death. If it lead to death, then that would invalidate the conscriptors claim that without the conscriptees help, they could be destroyed. They wouldn't kill the only hope they had to stave off destruction. If they did, then it would prove that they didn't really view their destruction as eminent without the aid of the conscriptees.
Imprisoning the conscriptees now would invalidate the conscriptors claim, in the same way that killing the conscriptees would. As well, they wouldn't do it for the same reason, that is, they wouldn't imprison their only hope for survival without disproving the legitimacy of their original claim. There final option is to threaten that the conscriptees would be imprisoned after the conflict, if they did not give them aide. After the conflict, either everyone has been destroyed (or enslaved, etc.), or they have survived the attack. If they survived the attack, this too would invalidate the claim that without the conscriptees' aide, all would perish. All have obviously not perished. They would be unjustified after surviving the conflict without the aid of the conscriptees to imprison them on the basis that they refused to aid the conscriptors' eminent destruction, because their destruction was never eminent without the aid of the conscriptees. If everyone was destroyed or enslaved, enforcement of the threat of imprisonment is impossible, thereby becoming null and void.
What has been shown is that in this rare, limited case, military conscription is unjustified. And because this was the only case that supposedly justified military conscription (I haven't heard of any other that wasn't founded on bigger fallacy), now that it has been shown as unjustified, all military conscription has been show as unjustified.