I remember an incident when I was living in Japan where something went wrong at work and someone sent out an angry email asking “Who is to blame for this!?” It’s a pretty common question in a Japanese workplace. People are expected to be perfect and to never mess up. The way you prevent issues is by getting rid of people who fail.
Of course, the reality is that everyone messes up. We’re not computers and we’re not able to control the wider world. Everything is a gamble, to some extent.
The better, non-Japanese way, of dealing with a problem is to investigate what happened and see if there’s a way to mitigate it. Yeah, there might be a person who is just a dumbass, and the solution might be to fire them or castigate them or whatever, but maybe the problem is that we need better lighting or better data or something else.
The problem of slavery is basically that people suck. The people in the North or in England or wherever else were pro-slavery so long as it was in their economic interest. Once they could live without it, morality kicked in. Humans have been enslaved and treated horribly throughout history.
There were probably instances in history where slavery and serfdom could have been knocked out, but (I think) a side effect of the belief in the divine is that it raises the potential that some people are better/holier/cleaner/etc. than others. Without divinity, you could have been born into any position in the world, with any arbitrary talents and capabilities. With divinity, if you’re born to a Lord, you are also a Lord. If you are born to a slave, you deserved it or the gods chose it for you out of some grand design.
Ultimately, the way to mitigate our humanity was the invention of paper and then the further invention of the printing press, which allowed smart people to debate and to publicize their ideas. A few people were able to make compelling arguments for humanist morality - where all people have a fundamental value that is equal between everyone. But even then, it took until market forces allowed a change to happen before the change could happen.
So who to blame? Who cares.
Let’s just be glad that it ended and focus on making sure that similar things aren’t happening in the world today.
Just in case you aren’t aware, Roots is effectively a work of fiction. The first generation in the book are inventions of the author (or his editor) and have no basis in reality. Later people in the book may be based on actual ancestors of the author.
Much of the work was plagiarized as well.