The case of Gillette v. United States in 1970 revolved around the issue of conscientious objection to military service during the Vietnam War. The petitioner, Guy Gillette, along with other individuals were convicted for refusing induction into the armed forces on grounds that their objections to participation in war did not meet existing statutory tests for conscientious objector status because they opposed particular wars rather than all war. They argued that this violated their First Amendment rights by discriminating against certain religious beliefs and denominations which only oppose unjust wars but not all wars. However, the Supreme Court upheld these convictions ruling that a law exempting from military service persons who oppose "war in any form" does not violate Free Exercise or Establishment Clause of First Amendment even though it disqualifies those whose opposition is limited to particular conflicts. The court found no evidence suggesting Congress intended to accommodate selective conscientious objection and concluded there was no unconstitutional discrimination against religion since non-religious objectors would also be disqualified under similar circumstances.

In the dissenting opinion for Gillette v. United States, Justice William O. Douglas argued that conscientious objection to war should not be limited only to those who object to all wars on religious grounds but should also extend to individuals who oppose specific wars due to moral or ethical reasons. He contended that the majority's interpretation of the Selective Service Act was too narrow and discriminatory against non-religious beliefs, violating both First Amendment rights and equal protection principles under the Fifth Amendment. Furthermore, he believed that a person’s opposition towards a particular war could be just as deeply rooted in their conscience as an individual's general opposition towards all warfare based on religious beliefs.