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"b. Government may substantially burden a person's exercise of religion only if it demonstrates that application of the burden to the person—
(1) is in furtherance of a compelling governmental interest;
and
(2) is the least restrictive means of furthering that compelling governmental interest."
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This is much less binding than the first amendment: "Congress _shall make no law_ respecting an establishment of religion, or prohibiting the free exercise thereof"
The constitution provided no exceptions whatsoever. By definition, a law which adds exceptions has moved the bar textually. It is, by definition, unconstitutional.
Again, it was a bad move by conservatives using liberal laws to protect themselves, rather than just pushing for conservative laws.