At least, according to this:
The mere fact that the team was making a game with slavery as a theme was an intentional choice. There are films in which ‘fun’ is not the emotional goal, such as Django Unchained or 12 Years a Slave, and Giard wanted to tap into emotions like righteousness and revenge as motivators instead of mere pleasure. “Strong emotions can be more important than only positive ones,” Giard said.
…because I am enjoying the living f*ck out of sneaking up behind slave overseers and killing the bastards. Or driving them berserk and watching them kill each other. Or throwing them off of tall buildings. Or… well, you get the idea.
PS: For the record, it bugged me in the main game when I’d raid a plantation, but couldn’t liberate the slaves in the process.