Well i'm not expert but i try to do some renders in free time for my own and for some games i play, then post it.
I know my work is not the best but i post it for the fun and also if there is an advice i could get it will help me improve.
Depends really there are only two or three fan threads that i did go and see so, maybe the way you see it "ruin it" i didn't see it on these two threads (the third one is the main artist thread so not about games more about someone actual work)
I think what DS means (I could be wrong but have seen it myself) is that you will at times see characters in rather 'interesting' scenarios that would never happen within the context of the story they have come from...and many of those can be how to say, a little disturbing. Like I said, doesn't bother me personally but can be offputting to say (as a pure example) seeing Viola surrounded by 5 BBC's while in bondage. Get what I mean?
For something like Anna Exciting Affection, I love fan art like that, because it fits within the framework of the character.
Edit: This is important to many, as has been said before in other places, you become emotionally invested in certain characters, otherwise, if you didn't, why are you even bothering with it? This applies to VN's, books, graphic novels, films...TV shows....