Given that most black Africans (AFAIK) were sold into slavery by other Africans, it's not a given that their lives were better in Africa than they were later in America.
Even if that is true, that does not make the forced migration and continued subjugation of slaves in the American South through the 19th century any less deplorable. Slavery is slavery. Your implicit acceptance of the "lesser of two evils" for something as serious as slavery is disturbing. We aren't even talking about the "hidden" conditions of working poor in foreign countries, we are talking about institutions that have visible cultural, economic, and social ramifications in present day America.
EDIT: I hate to use Wikipedia [0] as a substitute for substantive discussion, but your point seems to toe the line of being a false dilemma. The power/money elite in both the 19th century and the 21st century clearly have more options then just: leaving slaves in Africa/having very bad working conditions in Asian fields and farms on one hand, and bringing slaves to America/having marginally better working conditions in Asian factories, on the other hand.
Be disturbed then. It's possible, and in my view necessary, to rationally compare two non-optimal alternatives, even if an even better alternative is both possible and probable. As Aristotle allegedly said, "It is the mark of an educated mind to be able to entertain a thought without accepting it." And discussing a concept doesn't imply accepting/endorsing it.
While one might be able to give a fair and balanced take on "non-optimal alternatives," I frankly believe that a bad idea, or at least bad historiography, doesn't deserve a very big seat at the table of discussion. You paint the argument as a contrast of two, and walk away from the conversation: that's not a very rational, nor fair, comparison.
...while we are quoting Aristotle:
"Since then some men are slaves by nature, and others are freemen, it is clear that where slavery is advantageous to any one, then it is just to make him a slave." [0]
Clearly "entertaining thoughts without accepting them" isn't enough on it's own to lead to sound, just and fair policy-making or historical narratives.
It was also partially a race/tribe issue. White people like to forget that "blacks" actually aren't simply one big homogeneous group, especially not in Africa -- neither ethnically nor culturally. Just look at the Rwandan massacre for an example of ethnic clashes.
EDIT: I hate to use Wikipedia [0] as a substitute for substantive discussion, but your point seems to toe the line of being a false dilemma. The power/money elite in both the 19th century and the 21st century clearly have more options then just: leaving slaves in Africa/having very bad working conditions in Asian fields and farms on one hand, and bringing slaves to America/having marginally better working conditions in Asian factories, on the other hand.
[0] https://en.wikipedia.org/wiki/False_dilemma