Prior to that, it may have been wrong but it was not a criminal act to own slaves in the the southern states of the USA though in the northern ones it was not legal. That is the difference between fact and editorializing, and a proper historical reference should differentiate between the two. Because white racists have their 'narrative' too, which goes something like this: 'Blacks were uncivilized primitive pagans and we did them a favor by bringing them the benefits of western civilization and Christianity - take a look at the Congo, Sudan and Angola if you have any doubts.' Should that narrative be presented as equally valid when teaching about antebellum Southern society? Or should we maybe stick to facts like the legal framework of slavery, the conditions on the slave ships, numbers who died in transit, economic impact on African societies, economic impact on Southern society, historical context of slavery (such as, for example, that slavery continued to be legal in some Arab countries as late as 1963 - and no that's not a typo -nineteen sixty three was the year that JFK fourced the Saudis to abolish it) and leave the reader to make his own moral judgments without inserting editorializing into the text.
U.S. confirms ISIS computer expert killed in air strike (Reuters)
from the article: PA adopts textbook, banned in Israel, offering both sides' narratives