Why did Antonin Scalia’s opinion in Employment Division v. Smith upset some conservatives?

Antonin Scalia’s majority opinion in Employment Division v. Smith (1990) upset many conservatives because it reduced the level of judicial scrutiny applied to government restrictions on the free exercise of religion.1

Prior to this ruling, the Supreme Court had utilized the "Sherbert/Yoder test," which required the government to demonstrate that denying a religious exemption was necessary to achieve a compelling state interest using the least restrictive means possible. By rejecting this test, Scalia’s opinion held that the First Amendment’s free exercise clause does not constitutionally require legislatures to grant religious exemptions from generally applicable laws.21

For many conservatives who prioritize the protection of religious practice, this decision was seen as a significant weakening of constitutional safeguards for religious liberty, as it shifted the burden away from the government to justify its interference with religious conduct.12