Slavery wasn't invented in America. It was common during the Roman Empire and thousands of years before that. Blaming 18th century folks for not righting every wrong up to their time is lazy, as it would be to attribute full-responsibility to you today for something improved and looked down upon in the future.
(None of us are fully independent but gain and suffer inertia from history and society at large.)
Still, we can learn from Ancient Greece, American Founders, as well as folks today.