Duty to your country.
It's not demeaning or dehumanizing, it is service your country is calling upon from its citizenry. This is a two way street, nations serve their citizens and citizens serve their nation, voluntarily or when called on. We've lost that in recent decades and have been draining the fuel tank of national cultural virtue without putting anything back in, it's time to top off the tank.
I know that it (mandatory service) has never been perfect, the wealthy and connected sometimes got deferments or preferential postings thru unscrupulous actions but that doesn't mean that concept of mandatory service, specifically military service, was not overall beneficial to the country, directly in acquired military manpower required or indirectly in other ways (character development, intermixing of normally disparate groups, a unifying experience shared by generations, etc...).
I see your point but mandatory military service is not forcing someone to perform economic activity from which someone else will profit (that's slavery) this is service to the nation.
Honestly, I don't think we (the military) really need it and it may not have the effect some of us would hope it would have on the youth impressed into service but I would not dismiss it out of hand.