Slavery existed since the beginning of time. Clearly people sought freedom and slave revolts were common. But that is quite different than a government and society deeming that "owning" slaves was evil.
Which countries abolished slavery before western nations forced them to? Which nations continue to ignore the existence of slavery. Understanding how your value system has been shaped by western values is helpful in understanding you are no longer African. You are a Westerner.
My father-in-law often tells my wife, that she should not return to Indonesia. She may have been born there, grown up there, but after nearly 40 years in America married to an American, she is not Indonesian, she just looks Indonesian. That is the truth.
Many of your ancestors came from Africa. But humans are tribalistic. And since you can't be "African", you want to belong to a new 'tribe" with its own distinct history, culture, and traditions. And so, you need slavery to be taught as part of "African American" history to build identity, something to claim as a "bond". Like Jews recounting their history during Passover, slavery becomes something "special" to help set African Americans apart.
To promote this separate identity, it has to be defended. No Christian can understand what it means to be Jewish. No African American can understand what it means to be Native American. Every separatist movement has to create needs a basis to argue why they need to preserve their traditions, culture, and history and teach their children... less they ever forget.
But actually, forgetting is a good thing. There is no doubt some of my ancestors were slaves, there is no doubt some of them were Nazis, some of them were slaveowners, some of them were probably Jewish, but none of that defines me. I do not identify with those experiences; I identify with patriots fighting to create a new Nation more than hundred years before my first ancestor touched US soil. I identify with Abraham Lincoln taking this country one step closer to "the dream". I identify with MLK, taking America one step closer by insisting that until civil rights were the same, we would never be "equal". Notice the word "we", that includes you.
You may or may not realize that you are struggling to preserve a unique separatist identity. My guess is you would allow Obama to join this group even as his father was African and his mother descended from slaveowners, as long as he identified as African American and embraced the history, culture, and traditions of "African American" history. If you can "fit" him in... he is in. African Americans commonly refer to Obama as the first African American president, even though Obama said when running that his skin color does not define him. Every group needs its role models, so their children can grow up and be like them.
Simply said, you are trying hard to use slavery as a key part moment in history that helps define African Americans and anyone with the right skin color is welcome to join if they identify with that history even if it did not impact them. Part of the problem is immigration, integration, time and success is undermining the African American as an "identity group". And so, you need to recruit children by promoting separatist ideology while they are young or the young will end up like me... identifying as American (my mother came off the boat, but I simply don't identify as German).
