Slavery was doomed to die a natural death in only a few years anyway.
As a British person would say: "Bullocks!" Where's your source? Here's mine to counter this ridiculous claim:
1790: 697,681 slaves - 8% of blacks are free.
1800: 893,602 slaves - 11% blacks are free.
1810: 1,191,362 slaves - 14% blacks are free.
1820: 1,538,022 slaves - 13% blacks are free.
1830: 2,009,043 slaves - 14% blacks are free.
1840: 2,487,355 slaves - 13% blacks are free.
1850: 3,204,313 slaves - 12% blacks are free.
1860: 3,953,760 slaves - 11% blacks are free.
http://en.wikipedia.org/wiki/Slavery_in_the_United_States
There is absolutely NO indication that "slavery would have died a natural death." At least not for another 100 years before mechanization of the farm comes about due to an efficient and small internal combustion engine. No indication whatsoever. None. This revisionist history ******** has to stop.