I think the most problematic RPG I'd like to run would be a less British take on Space 1889, in which the players serve the Emperor, trying to carve out a spot on Mars among other colonial powers racing for "a place in the canals," and facing attacks by Shinsengumi nationalists.
This would be very much The Splitting Up of the Melon on another planet; our heroes wouldn't necessarily be the good guys, here.