So just to check, you'd be cool with backer messages that included racial slurs as well?
eta: wait, you probably meant the backer NPCs, not the memorial message, didn't you?
Oh just stop it with these silly falacies. You cannot win an argument by trying to misrepresent someone else's position.
If a backer message featured ingame lore friendly racism, then yes that would also be ok.
More about removing a joke that targets an oppressed group and was painful to some of its members to encounter.
Can you prove that said joke was made to target anyone in particular? Unless you can then I would be more careful when making such accusations. You, and some others, have apparently convinced themselves that the joke is somehow an example of great social injustice. It's not. It's a single joke in a video game. If they remove that poor joke then they might as well remove all of the other poorly worded backer messages or all other instances in the game that may offend some people. Like the hanging tree, incest etc.
If you want the joke removed then you better be very precise in your definition as to what would warrant a removal from the game.