Many people confuse slavery of the antiquity with slavery once prevalent in Western Hemisphere economies.
American slavery was referred to as “the peculiar institution” because unlike slavery in ancient times, slaves were treated like livestock…traded and sold, splitting mates, siblings, parents by selling them separately, even breeding them like farm animals. This is not how slaves were treated in biblical times.
Like the church teaches us, we have to consider the cultural context when written…those making the claims you speak of are not adhering to that principle.