An organized, disciplined military is more effective at defending against an organized, disciplined military.
That's true. The thing is: defending what? The country? The government? The king? Going to war is trading my (relative) safety for theirs, and I've never been too fond of them really.
You are right, your indivudual chances of survival increase by not enlisting as a soldier. At the same time, our collective chances of survival (that includes your parents, children, etc) decrease when young people walk away from the fight.