Be that as it may, mono black is without a doubt terrible as an aggro deck. The problem with black is that other black decks also want tutors, discard and removal. Its best creature, Phyrexian Obliterator, can be killed by any number of cards without gaining any value, and the smaller creatures can't match white, green or red. Red has similar creatures, but it has reach which can double as removal.
The only time I've had success with a black aggro deck was a B/W Death & Taxes style deck. I've also had success with U/B which was more aggro control and B/R which was more mono red splashing black.
Like you said, aggro needs redundancy and black lacks that because other decks leech off the black cards. Then there's the fact that black historically never was an aggro powerhouse. The only time I can remember was when Hatred was around. Randy should add Hatred!