These people knew the possible consequences of their action, they did not believe there should be such consequences but they performed the same contract all of us who do illegal things do. We agree that we have weighed the balance between benifit and cost and have decided that it is worth our while, worth the punishment to do what we do. Slaves had no such oportunity - especialy those who were born into slavery, born, owned.
That contract - contracts you seem to believe in, at least somewhat, is the difference between a person in jail and a slave.