It is usually brought up in response to someone saying that the only logical thing for a slave to do is to support the invader.
Sadly, as evidenced even by today's headlines, people are not always logical about welcoming an invader, even if that invader is on a mission to free them.
The fact that free blacks owned slaves simply points to the widespread philosophical acceptance of slavery as an institution. Many were the arguments that the slaves were better off as slaves, than they had been in their primitive lives. This even has a familiar tone to it in that our civil masters think that they can decide what is good for us better than we can decide it for ourselves.
okay I understand. I think.... thanks.