Yes, that part of history has been swept under the rug.
Most slaves were treated well and as part of the family in many ways.
Basically the modern equivalent would be today’s household pets, many of which are treated like family, but some of which are horribly abused.
Imagine a future in which having pets is thought of as horrible, and all references to pets being treated nicely were wiped from the history books and only stories about dog fights and puppy mills and owners who chain and beat their dogs remained. That’s basically what has happened.
Somewhat similar to the maids housekeepers, nurses and gardeners in my family’s past. All were kept well and cared for through old age. I remember my grandmother’s nurse, Nernie who was also my father’s and great aunt and uncle’s nurse, at our dining room table each Sunday. Alice, my great grandmother’s housekeeper also took care of g-grandmother to her last day. She was then pensioned off and lived out her last days in her family with visits to ours.
In the Old Testament those who chose to remain had an awl go through their ear.
As you've mentioned, in some cases slavery can be a good thing. The wise master will protect his investment, care for it, and treat it with dignity.
Emancipation was poorly handled. As a tactical war move deemed essential at the time, it probably happened in the worst way possible, and society is still paying the consequences today.
You're analogy falls apart in so many ways. In the first place I can't believe you're comparing a human being to a pet dog. In the second place my pet dog doesn't have to work sunup to sundown. She doesn't have to worry about being sold. If she wanders off I'm not going to beat her. She doesn't have to obtain her own food.
It really was a horrible comparison on your part.