While it may be true that African Blacks have benefited from "the Americanization Process", it is not true that Slavery per say was good for Blacks in general.
You have to recall that Slavery was a big part of life in Africa at least 30,000 years before "the USA slave trade".
In point of absolute fact, African black tribes never had a substantial Navy. The reason for this was thousands of years of abuse from North African Slave Traders. In fact almost all the world suffered from these despots. They had faster better armed ships that until recently nobody understood, lest of all the less well generally educated African states. It wasn't until the use of super-ships with long range canon that the Europeans got a "hang" (from the yard arms) on the slavers of North Africa. Chinese peoples weren't safe until years earlier they developed rockets that could set slaving ships on fire at long ranges; even so, a sneak attack was never out of the question with North African Crab Claw rigged sailing boards with siege crossbows.
Our Marines don't sing about Tripoli for nothing you know.
Who knows what these industrious peoples might have done without such "competitive inhibition".
I would argue that US slavery was primarily driven by the moral argument against the British idea of mass murder by proxy (such as with the arming of the Zulus by selling them and only them pig iron resulting in a massive disparity of arms and the extinction of God only knows how many peoples). Slavery was simply put the most economically feasable means of protecting the most they chould from homicide.
But, after several "slave revolts" and the loss of many of those that gave everything they had to save a few ingrates who did not understand why they were taken and much less wanted no part of any such understanding, there were very harsh rethinks as to the needs and practicality of reformation of and for these "lost souls".
What would you have done? Say you saw a black fellow kill all your family after they saved him from certain death by investing all they had in rescuing those people through use of the most sophisicated technology of that or any age before it (sailing vessals and the navigation to sail them). Say they certainly could have used those vessals for other routs for decades, but would instead use them on a few frantic trips into worm infested waters, where those massive investments were certain to be lost to said worms. Say that because of the vast expence of throwing away ships to save blacks they had been cruel; say they knew the blacks did not and would not commit to their hearts any understanding of this cruelty, but continued openly to fume at those they all saw as inhuman. Would you have given those people the means to fight your soldiers ~ knowledge ?
Given the fact that even today the europeans encourage mass murders by supplying one and only one side of a conflict with arms, would you have treated those Black people as a means to save at least a sample of the rest? Or would you abandon those left to their fates, free the slaves at your peril and those of their comrads and former neighbors?
Was slavery wrong? Yes. Would more of Darfour have been worse? Yes.
Your fellow is correct, we don't live in a perfect world. And when outcomes are improved by what may seem unlikely generosity, one should have the grace to say so. But on the other hand, slavery as an institution is wrong.
Thus I disagree with de@dbeat dad laws. Does your fellow? Or has he modified his abhorence to slavery when he sees it might eventually be his race holding the reigns, whipping ours?