The author should note her article is accessible world wide not just the USA. So putting slavery as a literally black and white argument makes sense in her country but not universally. The important point is universally — wikipedia lists 50 great empires and all of the pre 20th century ones had slavery (and also women as the chattels of the father and then the husband).
Take my own origin in East Anglia (UK) — Boadicea objected when the Romans declared her part of Mercia a slave province. They stripped her and whipped her as they raped her two daughters. It led to a major rebellion which ended with Boadicea led in chains through Roman. For over 500 years Arab slave traders raided the west coast of Europe up to and including England to take slaves. China had slaves. India had slaves. The Mayans and Incas had slaves. The bible talks of slaves (one of the justifications used for slavery). And even when slavery ended in USA Russia had millions of serfs with just the same rights as any slave. Slaves came in all colours, all races and perversions of all major religions.
Check out the Index of Slavery website; there are as many slaves now throughout the world as pre-civil war USA. And that includes my own country of New Zealand where the estimated number of slaves has increased by 200 in the last decade. I leave it to you to check out the figures for USA, Canada, etc. We need to keep affirming the equivalence of all people and stop the argument used by almost all slave owners that their slaves are some kind of inferior creature.
Thank you for an article that introduced information I hadn’t known about Jefferson. I suggest you judge him by his time and on that basis he wasn’t as clearly sighted morally as Tom Paine but I think he was a better than average human so condemn his mistakes but not his entire existence. As they say judge carefully since we will all be judged eventually.