It was mentioned that the curriculum made the claim, and some agreed with that.
I'm glad you posted what you did. Too many oversimplify issues and end up missing important points.
That is indeed the problem. People want to push an agenda rather than look at the complex reality. It wasn't white man bad, black person good - it was a whole bunch of people doing things as they saw their interests according to norms at the time, some of which we find awful today. Whether it was Dutch slave ships, African tribal warlords and costal cities, American plantation owners (white and black), all were part of the process. We really should study the full history and discuss and debate what it would have been like to be in that time and play according to the rules that existed then. Some slaves did not have it that bad actually and might have even been preferable to starvation and squalor (more common back then than you might think). Some slaves lived in such hellish conditions, its hard to even comprehend. But to be honest, life in general, was much shorter, harder and more brutal for everyone back then.
Slavery has existed everywhere and for as long as humans have been organized into groups. Peoples have enslaved others because of debt, losing a war, "lesser" races or clans, crime, so many things.
To me, the most terrible thing about slavery in America, however, is that it trained whites to think of themselves as superior because of their race and trained blacks to think of themselves as inferior. This pernicious lie permeated our society and obfuscated the true source of America's strength. It is in our culture that made us superior. To quote Tocqueville, America is great because it is good. Those who thought instead it was because they were racially superior or inferior allowed the culture to rot and our goodness - and as our Godliness has dissipated, so has our strength.
Only the most delusional white Americans today think they are superior simply because of their race, yet far too many black Americans still believe in their heart of hearts the awful lie that they are inferior by birth. Rather than recognize it is a culture of victimhood (rather than hard work, excellence and Godliness) that keeps them in chains to the political hucksters that claim to represent them.