Personally, I look at it like this - if there is established lore on the subject, do not alter it in any way. Also, accept that Blizzard changes the lore every time they release an expansion or a book, and that your character’s backstory may change at any given moment to compensate.
That being said.
If the lore is flimsy, or otherwise fails to offer comprehensive information about a subject, players should be able to fill in those gaps without having to suffer scrutiny. In regards to the Church of the Light, while, yes, the majority of the Church despises the corrupting power of the Void, they have made exceptions to unseemly practices in the past. Do not forget, during the emergence of the Scarlets and during the assault on Northrend, many priests and paladin were suddenly a-okay with all kinds of otherwise uncouth individuals and their practices.
Plus, you know, in general, how about people not be a dick and let others RP however they want? I mean, if it is not a major lore violation like, saying, admitting you are Varian’s cousin, or that Lor’themar buys male hookers and you were one that he purchased, then is it really so upsetting that you have to trash someone’s RP? Just go with the flow, man.