Instead, I'm speaking to finding out what the player goals for the table actually are, and then running that game, if it's something that can be agreed to.
But, my recommendations are not to put the GM foot down, but to find a consensus as to what game everyone wants to play.
And if consensus can't be found (which your first quote seemed to admit to as a possibility) do you capitulate or do you not have that player play?
It feels like for every DM there are things that aren't worth discussing. (Explicit sex? Rape? The party becoming slavers? Making a Third Reich parody to go after half-orcs?). Is there nothing you would just decline to discuss because it's on your list of things you don't want to RP? For some, could murder hoboing reasonably be on that list?