A more thorough explanation:

Engel v. Vitale is a Supreme Court decision from 1962 that banned prayer in public schools. The case was about whether a public school could have classroom prayers at a time when America was becoming more diverse and secular. The decision was controversial and unpopular, with many people protesting and calling for the Supreme Court justices to be impeached. However, the decision reflected a changing America that was becoming more pluralistic and less dominated by Protestantism.

The legal argument in Engel centered on the First Amendment's Establishment Clause, which says that "Congress shall make no law respecting an establishment of religion." The Supreme Court had previously applied this clause to state law, meaning that states could not establish religion either. The question in Engel was whether a public school prayer, even if it was optional and not tied to any particular religion, violated the Establishment Clause. The Court decided that it did, because any form of prayer promoted by the government was inherently religious and therefore violated the principle of separation of church and state.

The Engel decision was controversial because it reflected a changing America that was becoming more diverse and less dominated by Protestantism. In the past, public schools had often promoted Protestantism, but as America became more pluralistic, this became less acceptable. The Engel decision reflected this changing reality and helped to establish the principle of separation of church and state in public schools.