Slave has a very powerful specialty skill. The conwith being a slave is that you are a slave. That will (or should at least) affect any type of social interactions. At least with your own ark. So if you think it is fine that slave doesn't have that con do it.
I asked my players if they wanted to have slaves in the ark and they said no, so we don't have that role in the players ark but there are other arks and they might be slavers. In fact my players have met some mutants from another ark. So if any of my players wants to play a slave they might now do so. He simply is a runaway from the other ark. The con in this case is that any social interactions with that ark will be really bad (they want their property back).
This way, it is still a disadvantage to play slave, because it will be difficult to maintain good relationship with the other ark (the slave's ark), but at the same time the players can act normally (or as normal players can act) in their own ark. Also this might also lead to some interesting adventures.
“I’d say thistles, but nobody listens to me, anyway.” - Eeyore