By and large, the issue with controversial content isn’t the problem of slavery, bigotry and the like in and of themselves, but rather how they’re handled.There has been a movement to remove controversial content from games for a long time. It has been openly discussed since the days of the Internet starting and probably was before that, but it was a much more local discussion.
For instance: It’s one thing to include a slaveholding society in your RPG, it’s quite another to have the slaves depicted as happy with their lot in life or illustrated in ways that mimic RW racist imagery.
It’s also problematic to whitewash cultures when you’re trying to include them in your game. The 2Ed full color Caucasian pharaoh and queen as a splash page in the Egyptian pantheon not only eliminated the ethnicity of those who should have been there, it also put the white rulers atop a culture that unquestionably practiced slavery.