Zacs-Master - "Andy, I'm not sure using the word slave is racist."
Use of the word per se is not racist, but insults are all about context.
If I say to a black person in discussion, some black people used to be slaves, that is not a racist comment, it is a statement of fact.
If I say to a black man I don't know on a tube in an argument, you have a problem because you guys used to be slaves, that is an insult, and a racist insult at that. The insult is saying that the man has a problem, the used to be slaves' reference is used in respect of his skin colour, and is a racist comment.