Characterizing the argument as being against "fictitious people having fictitious feelings" is missing the point. The "world's context" is entirely whatever Obsidian wants it to be. Presumably Obsidian curated the backer memorial pledges and had rules about what could and couldn't be put on them, and I think people are mad that they didn't see anything wrong with this one. If the limerick served a purpose other than just being there because someone paid $500 for it, then I think there would be less of an outcry.

There's a character named Durance in PoE who is a a xenophobic, sexist dick, who says things that are way more objectionable than a throwaway transphobic limerick, and I haven't heard anyone complain about him at all, but he's also a fully developed character whose views and ideologies can be explored and discussed throughout the game.