If this was a video documentary and not a video game it would not even be an issue. It is not supposed to be 'fun', it is meant to be 'engaging,' just like a good documentary. Also, it is not meant to cover everything exhaustively, nothing could ever do that. Also, it is not meant to replace a teacher, but to augment their ability, just like good documentary could.
To me, it doesn't matter if it is a 'simulation' or 'game', both are used (practically interchangeably) throughout education systems. This, like Oregon Trail, use a virtual environment to allow one to see some of the choices, conditions, environment, and dangers of living at a certain point in time with focus on attempting to make the considerations relatively realistic. The whole anti- #slavesimulation crowd is just another race-bating attempt at bringing more argument to social inequality. If they wanna ban this game, then I guess we should ban Disney's Pocahontas and hundreds of other educational tools / mediums that deal with slavery. The reason why the US educational system has gone from great to horrible is because of frivolous arguments and road blocks such as these, leaving very little room to teach our youth important facts and think critically.