@cwebber The "immutable" requirement is such a strange US-specific legal artefact. First, religion is considered a suspect class, and thus subject to strict scrutiny. One’s religion isn't immutable though, so that's not actually a requirement!
And second, during the gay-marriage debates of the early 2000s there was a fascinating split in how US and European activists framed being gay. In the US you often heard "I was born this way" and a strong emphasis on gay-ness being innate. Because in the US context – against the historical backdrop of race – that's how you are awarded rights. But in Europe the rhetoric was almost the opposite, emphasising freedom of choice as the basis for rights.