There is a church, and a Christmas service, in Harry Potter and the Deathly Hallows, and although they have a Yule Ball in Harry Potter and the Goblet of Fire, the winter feast at Hogwarts is generally referred to as "Christmas". Also, since we apparently agree that the potterverse is just like World One unless stated otherwise, all kinds of Christian and non-Christian denominations exist there, including the ultra fanatics the Prayer Warriors are based upon. Thus, you cannot charge for "uncanonical-religion is never mentioned in Harry Potter's world", or for shoehorning something in that implicitly is already there (and probably one of the reasons for the International Statute of Secrecy).
Better pro-mission arguments would be:
- This version of Hogwarts needs to be burned strictly based on being an uncanonical straw-castle filled with pumpkin-headed straw-men. The actual dispute in which these straw-men are used doesn’t matter at all.
- The Department of Technical Errors could have a feast with this, without actually discussing the content (except internal continuity).
If you can restrain yourself, and are sufficiently skilled to write agnostic, genderless, alien agents who genuinely don’t understand misogyny and homophobia, don’t care to comment on the human’s beliefs, and leave judgement of anything that the Prayer Warriors claim to be commanded by their god (yes, that includes the cruel punishments that so upset you) to the Spanish Inquisition or whoever may feel fit to act as a scripture canon expert, you may be able to write a decent mission. But I’m not sure whether you would have fun doing it this way, and if you don’t have fun doing it and the community doesn’t want to see it done anyway, you better shouldn’t do it.
(Note: I’m agnostic, so this is none of my concerns, but the Spanish Inquisition might well have decided that claiming to be a prophet chatting with Jesus is blasphemous and that the heretic should be burned on the stake.)
HG (who MST’ed "Hogwarts School of Prayer and Miracles" in the 2014 badfic games, because that’s the place to where I take my Bad Ideas)