Athenian Slaves were usually pretty well treated, admittedly there were areas of slavery that could be very harsh i.e. silver mines but on the whole the life and experience of an Athenian slave would have much better than that of an African Slave in the USA.
Roman Slaves were very similar to the Athenian slaves, often they earned or bought their freedom (they were paid) and when they didn't they could find themselves living very comfortable lives. An urban slave would have a better quality of life than a rural citizen.
In the case of Ancient Slavery YES there was serious hardships and terrible conditions for some slaves, however it was nothing like the slavery experienced by the African peoples.