The issue of mandatory vaccination is a thorny one for libertarians, writes Dr. Jeffrey A. Singer. A tension exists between the rights of the individual and the rights of the general public. No person should be forced to have something injected into one's body—whether or not it is potentially harmful or life threatening. On the other hand, other members of the community also have a right to be free from force. And a threat to their health or life by a person carrying a highly contagious disease can be a form of aggression. The challenge lies in achieving a proper balance between the rights of the individual and the rights of the general public to both be free from aggression.