Providing facts should never require justification. Everybody is free to have their own opinion, everybody is not free to have their own facts.
Regardless of the above, I'll indulge you because this is a topic I find particularly interesting - and there is also a moral. It seems many people in society are starting to view things as caricaturizations of reality. There are the good guys, and there are the bad guys. And the person I was responding to, I suspect, likely viewed the transatlantic slave trade through this lens based on his apparently significant offense as somebody daring to use the word 'just' in reference to a time frame of slavery. I think this is surprisingly dangerous.
The reason for this is that in reality things are not caricaturizations, but changes that might not seem so severe to many. For instance back on the slave trade I hope you'll indulge a few more of those condemnable facts. In the entire transatlantic slave trade about 12.5 million slaves were bought from Africa, with 10.7 million surviving the voyage. Of the 10.7 million 388,000, or about 3.6% [1], ended up in what would be the United States. Many people in the US seem to think that slavery ended, more or less, after the Civil War. That's obviously quite a poorly informed view, but it's built upon this caricaturization of slavery. In reality today there are more slaves than ever before in history with an estimated 45.8 million people enslaved worldwide [2]. That includes an estimated 57,700 slaves even within the United States.
Rather than judge people and events, I try to understand them - try to put myself in their shoes and see how things played out. And in this case, it's not hard to see. Slavery was likely a story of apathy and cognitive dissonance. In the US about 1.4% of free Americans owned slaves, about 8% of families. [4]. Obviously more owned slaves in states where slavery was legal, but I'm considering the entire population as slavery was a rich man's game - and getting involved in the business was little more than a carriage ride away. Similar to today how California's ratio of entrepreneurs cannot be considered in isolation as the lucrative opportunities there draw in people from across the entire country.
And those that did choose to own slaves likely convinced themselves it was morally fine since they were buying people who were already enslaved. In Africa at the time slaves were even subject to things including human sacrifice. [5] Just in West Africa there were events including the regular sacrifice of hundreds of slaves and on rare occasion even thousands at once. The cognitive dissonance there is not really hard to see.
And this behavior of cognitive dissonance and apathy continues to this day. Do you really care about slavery? I imagine we'd all like to think so, but reality paints a less favorable picture. What if the president started implicitly condoning slavery for his own benefit? You might think you'd care, but that has already happened very recently. Malaysia is one of the worst places for modern slavery. You can see from the aforementioned link [2] that about 0.4% of their population is a slave. That's one out of every 250 people for 129k slaves in a country of 30million people. In 2015 Obama chose to remove Malaysia from a list of the worst human traffickers. He did this just so he could squeeze them into a trade agreement he wanted to pass (the TPP). This was the same year that more than numerous mass graves and trafficking camps were discovered in Malaysia. [3] A few media outlets ran the story, but for the most part people showed they couldn't really care less. And so it almost certainly was during slavery as well.
What if I told you a list of companies or products that are still generated using slavery? Like chocolate? West Africa supplies about 69% of the world's cocoa. [6]. And unsurprisingly, slavery and even child slavery, is involved in its production. Companies funding the practice include Mars, Nestle, Hershey, and others. Will you now stop buying their products? Probably not. Think about that for a minute. A sweet treat is more important to you ("you" in this case is rhetorical, as even if you in particular would/will give up the companies - few would) than taking a stand against not only slavery, but child slavery. Slavery is incredibly offensive until it provides something we want, or when doing something about it might cause you some inconvenience. It's quite phenomenal isn't it? This disconnect between what we think we think, and what we actually seem willing to do based on that?
The point of this all is that I think if people were more aware of reality, and understood that the line between good and evil is far closer than any of us would like to admit, that we'd be much more inclined to concern ourselves with actual events and happenings - instead of taking faux offense at somebody using the word 'just' in a way you find offensive.
[1] - http://www.pbs.org/wnet/african-americans-many-rivers-to-cro...
[2] - https://www.globalslaveryindex.org/findings/
[3] - https://www.theguardian.com/world/2015/may/25/malaysia-migra...
[4] - http://www.civil-war.net/pages/1860_census.html
[5] - https://en.wikipedia.org/wiki/Human_sacrifice#West_Africa
[6] - https://en.wikipedia.org/wiki/Child_labor_in_cocoa_productio...