Second, be honest. Would you rather live in Africa or America?
This is a stuffty argument. If Africa was never treated as a place for Europeans to plunder people and resources from, it might actually be a decent place to live. People seem to forget that Africa is still recovering from decades of colonialism and the shock of having all established government and most infrastructure ripped out of the ground when African countries regained their sovereignty. Of course there would still be malaria, but you'd be surprised what actual houses and modern medicine can do to stem the spread of disease.
Barring an early end to colonialism, it's true that black people have it better off in the United States than in Somalia. But I'm guessing that if you told that to 18th century slaves, I don't think it would do much to make that experience any less horrible. It sure as hell doesn't justify it either.