Haley's Inability to Trace His Roots is the Real Tragedy
Yes, it was wrong of him to use another author's work within his own. Yes, it was wrong of him to allow the miniseries to perpetrate a hoax on the public which thought they were actually seeing him find his African relatives.
However, if you think about it, it demonstrates the most tragic part about slavery, the disconnectedness, the inability to have a family tree, to have basically no idea where you came from. A lot of African-Americans (or blacks if you prefer) don't even know what tribe their ancestors came from and that is the most basic identity you can have in Africa. It's what the oppressors (whether white or black) paid no attention to when they carved up the continent into countries, countries that often cut right through the area of land where the majority of a tribe lived, so that then tribal members might be living in separate countries.
As far as how truthful the barbaric acts of slavery in Roots, I would bet that stuff like that did go on. However, there were a lot of families with slaves who were not animals and, though they committed the sin of owning human beings, did treat their slaves as human beings and not as animals. That wasn't shown in Roots and it should have been.