Slavery in any form is an abhorrent abomination. It is a stain on this country's history. It matter not the least whether or not the slaves were comfortable or well cared for because the slavery itself was a poison to the spirit of both the slave and the slave-owner.
It is and always will be an indefensible evil.
It might not matter to you if the slave was comfortable and well cared for, or worked to death in the mines of ancient Syracuse, but to the slave I suspect it mattered quite a bit.