This quote is awful and Clinton should be criticized for its tone-deafness and skewed perspective. But the people making it akin to the Clintons owning slaves are pretty dumb. If you consider free labor from inmates to be akin to slavery, then we're all guilty of condoning slavery since our democratically elected government is responsible for setting up the inmate work system. Every time an inmate cleans your litter that inmate is your slave, according to this logic.
And honestly it's fine to feel that way. But if so you should be fighting your government to end the practice of inmate "slavery," not pretending the "slaves" here were Clinton's.