The abolitionists who were in favor of immidiate end of slavery by which they meant as fast as humanly possible they argued that there should be no other considerations which override the slave's right to his own life and freedom. There was another group which became known as gradualists who agreed with the abolitionists, they said it's true the slavery is wrong, it's evil, it should be gotten rid of, but they added on "eventually". What they argued was that should slavery seize immediately it would wreak economic havok on the south in particular but also on the northern industrial states which relied very heavilly on the southern agroculture. (...) It's important to know how the abolitionists responded to it. They did not necessarily try to argue that the immediate abolition of slavery would not have this terrible economic consequences. What they argued was - this economic sort of argument was irrelevant, because what had to take precedence was the right of the slave to his own liberty.

George H. Smith "Ethics vs. Economics"