the lunatic fringe

the ˌlunatic ˈfringe

(disapproving) members of an organization or group who are more extreme than the others; extreme groups: It’s the lunatic fringe of the Animal Liberation Front which smashes the windows of butchers’ shops, not ordinary members like us.The word lunatic means crazy. It comes from the Latin word luna, meaning ‘moon’, because people believed that the changes in the moon caused temporary madness.
See also: fringe, lunatic