They would have wound up as slaves back in Africa anyway.
That is absolutely not true.
In fact, in both Liberia and Sierra Leone, the freed "colonizers" immediately clashed with the natives because they thought, particularly in Liberia, that the natives were to become THEIR slaves. Still tension between the descendants of the freedmen and the descendants of the original inhabitants!
In neither case were the freedmen "dumped on the beach." Rather both of these places ... Liberia and Sierra Leone ... were well subsidized. ... and the "colonists" for the most part, were fairly well equipped and financed to begin their new lives.
The muslims could have sold them again.