The Thomas Jefferson Heritage Society and other authorities reject claims made that her fathered the children of Sally Hemmings -
http://www.amazon.com/Defense-Thomas-Jefferson-Hemings-Scandal/dp/0312561008
On your analogy to many trees in the forest, if slavery didn't exist in 1860, the Democratic and Whig Parties would not have split and Abraham Lincoln might not have been elected. There would have been no cause for Civil War (and no message board about it)!