Dude... you may not think it, but being able to join the military is a privilege. There is a reason the confederacy didn't let black slaves serve in the military with weapons, and it's not because black people were a privileged class they weren't willing to sacrifice. The ability to be a soldier is what keeps privileged classes in power. 

You think Iran picks members for their IRGC from the classes they oppress? No, it's picked from privileged classes that do the oppressing. Because the ability to fight and wield violence is a privilege that those in power have always jealously defended. 

And when the ruling class failed to follow this rule like in the case of Tsarist Russia, where they sent communist political dissidents to serve in the frontlines, they found themselves at the other end of the barrel. Turns out training the people you're oppressing in military tactics and giving them weapons isn't such a great idea.