It seems to me that any historical event that was both painful to the participants, and interesting to read and learn about after the fact, creates the same dilemma that's been discussed here. Will World War Two have been a net good if 10,000 years from now trillions of people have gotten incredible enjoyment from watching movies, reading books, and playing videogames that involve WWII as a setting in some way?

The first solution to this dilemma that comes to mind is that ready substitutes exist for most of the entertainments associated with these unpleasant events. If the Aztecs had built their pyramids and then never sacrificed anyone on them it probably wouldn't hurt the modern tourist trade that much. And if WWII had never happened and thus caused the Call of Duty videogame franchise to never exist, it wouldn't have a big impact on utility because some cognates of the Doom, Unreal, and similar franchises would still exist (those franchises are based on fictional events, so no one got hurt inspiring them).

In fact, if I was to imagine an alternate human history where no war, slavery, or similar conflict had ever happened, and the inhabitants got all their enjoyment from entertainment media based on fictional conflicts, I think such a world would have a much higher net utility than our own.