That's a really silly assertion.
The kinds of groups that you would consider "PC Police" would probably prefer that we INCLUDE slavery, since suppressing all references to it denies that it ever happened and could be construed as forgiving the crimes of those who committed slavery.
We excluded slavery because this is a game about romance and adventure, not the brutal realities of life in 1720. We also left out scurvy, malaria, impressment, dysentery, and syphilis. Plus, in a dramatic news flash, ships don't really sail directly upwind and crew don't magically regenerate.
We made the game we made to be a fun, piratey experience. Asking that it include the miseries of slavery is silly, and accusing us of kowtowing because we didn't make a game that included slavery is sillier.