It's curious how casually DiLorenzo dismisses the U. S. Constitution. The Constitution left the question of slavery up to the individual states. (Otherwise, the Southern states would never have ratified it.) DiLorenzo calls Lincoln's promise not to violate his oath of office the "strongest...
That's a lot more believable than the $1500 figure given in the original article. You are probably right that the $1500 includes insurance coverage that is not mandated.