The military does not get to decide which wars are valid and which are not.
The military does not get to decide whether we remain engaged in War A or B or whether we do not.
The job of the military is to execute national policy.
Well, why shouldn't they? Why not have, the first day of the war, anyone who wants to resign gets an honorable discharge that day if they don't think the war is just. sounds completely reasonable to me, and maybe our scumbag politicians wouldn't lie us into wars if they could.