I think that Joe Offer is maybe closer to the mark when he wrote, up the thread, "I see it as a song of nostalgia for the days of youth", rather than for any notion of nostalgia for the days of slavery - nostalgia which, given the date of the song (1860), would have been somewhat premature.

As for "Yet "Old Black Joe" implies that death was the only way that family and friends were parted from each other", that seems to me the wrong way round. Surely Joe is seeing death as the only way family and friends who have been torn apart can be re-united.

Rather from the song painting slavery as bucolic and happy, the implication I hear is that Joe is specifically presented as longing for death as a way of escaping a life of slavery and loss. The "gentle voices" aren't those of happy slaves, but of his dead friends and relatives.
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I'm wholly in agreement with what Jim Carroll wrote there - I would very much miss Azizi's contributions here, and I think the Mudcat would be poorer without them.