DiLorenzo thinks that it is a reflection on Lincoln's anti-slavery character that he supported the Fugitive Slave Act. But the Fugitive Slave Clause is in the Constitution, and Lincoln thought that any refusal to implement the right clearly defined in the Constitution would justify secession. You can't pick and choose which parts of the Constitution you like. Once you do that, then the Constitution is simply, as Jefferson said once, 'a blank sheet of paper'. Jefferson said that when he was contemplating purchasing Louisiana. And having said that by purchasing it he would make the Constitution a blank sheet of paper, he went ahead and purchased Louisiana.
The Real Abraham Lincoln: A Debate (2002)