Men do have a moral duty to fight to defend their country. This does not mean you HAVE to it only means its the moral thing to do (from my own moral perspective).
A moral duty to defend your country if called upon is not what allows the war to continue its the elected leader that gets to decide the war ends. Ukraine isnt calling up conscripts to extend the war, they are calling up conscripts in a response to increased russian troop numbers and to cycle troops off the battlefield so they can rest. Without conscription the war continues but the odds of losing are even higher.