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 … - Harry V. Jaffa

And comparing what happened in England—after all, in England the Parliament in Westminster was making laws for the West Indies. The West Indians didn't have any representation in the Parliament. The laws were made for them, and they had to go along with it. There was no such power within the Federal government to interfere with slavery, except by limiting the expansion of slavery. And it was Lincoln’s belief—and I think the best economic analysis that we have of the American economy in the antebellum United States indicates—that if the expansion of slavery had been ended, and if it was no longer possible for surplus slaves to be sold from the old states to new territories, that the pressure within the states to adopt programs of emancipation would become great enough to do that.

While slavery meant Egypt, and slavemasters meant Pharoah, America itself remained the promised land. The slaves knew that it was not in Africa, Europe, or anywhere else that a nation had been founded upon the self-evident truth that all men are created equal. It was their destiny to cross over jordan here, and to make their decisive contribution to the human story here, by partaking of that new birth of freedom that alone could vindicate the cause of all human beings everywhere.

And Lincoln said that by your own argument, if the local regulations are not forthcoming, you must support the federal enforcement; if you don’t, you’re taking the same position as the abolitionists, who denied any obligation to enforce the Fugitive Slave Law.