Mandatory national service is not just anti-liberty, it is un-American. Whether or not they admit it, supporters of mandatory national service do not believe that individuals have "inalienable rights." Instead, they believe that rights are gifts from the government and, since government is the source of our rights, government can abridge or even take away those rights whenever Congress decides.
http://thedailybell.com/editorials/35744/Ron-Paul-National-Service-is-Anti-Liberty-and-Un-American/