"Mandatory service" is not slavery because it is not the pure exploitation of man by force, but it does involve a surrender of freedom of conscience, of moral choice. Real service, real charity, does not need a government, or any other organization, to sanctify it. These organizations realistically threaten to corrupt whatever activities they support, both by fitting them into a national plan, removing initiative and choice from everyone involved (reducing them to the status of employees) -- and more importantly by destroying the spirit of charity and the meaning of the works themselves.

When the USA went to war with Japan, "conservation workers" in the Civilian Conservation Corps were used to build military infrastructure and to confine Japanese-Americans in "internship" camps. The CCC was run by military officers, with military-style discipline, and "desertion" was grounds for "dishonorable discharge." These young Americans did not sign up for the military, but the military used their involvement in "service" to capture their productive labor. It is not slavery, but it is something very wrong -- it is a deceit.

The ethic of the military as it has developed in America is in itself opposed to freedom of conscience, and for this reason it is opposed to the spirit of the foundation of the country, in which no significant standing army was imagined. Everyone can agree that a person dedicated to a military mission may have good reason to obey commands, to surrender his will -- in a non-moral way -- to the organization, so that it might act effectively. But a man who is made to serve a cause he cannot understand, or one to which he is actively opposed, is as a slave: he is not a free man, but is reduced to a mere body, without any will of its own to move it.

Thoreau refused to pay taxes to the federal government so long as it supported slavery. For this he was called an enemy of the nation, and put in jail. He served, not with his body, or even his mind, but with his conscience, by making a moral choice. It was by opposing the state that he served the nation. So long as the military does not allow this -- so long as the military pretends that a man can sign away his conscience with a contract -- it will remain opposed to freedom.