History: Why did some Northerners who disapproved of slavery oppose extreme abolitionism?

Answer 1

It seems that *most* Northerners opposed extreme abolitionism :

"The anti-slavery sentiment, which existed before 1830 among many people in the North, was joined after 1840 by the vocal few of the abolitionist movement. The majority of Northerners rejected the extreme positions of the abolitionists; Abraham Lincoln, for example. Indeed many northern leaders including Lincoln, Stephen Douglas (the Democratic nominee in 1860), John C. Fremont (the Republican nominee in 1856), and Ulysses S. Grant married into slave owning southern families without any moral qualms."

"Most Northerners favored a policy of gradual and compensated emancipation."

And the abolition in the Northern States *was* slow and gradual :

"The Abolitionist Movement set in motion actions in every State to abolish slavery. This succeeded in every northern state by 1804; although the emancipation was so gradual that there were still a dozen "permanent apprentices" in the 1860 census."

"On the ideological spectrum, from immediate abolition on the Left to conservative antislavery on the Right, it is often hard to tell where "abolition" (which demanded unconditional emancipation and usually envisaged civil equality for the free slaves) ended and "antislavery" or "free soil" (which desired only the containment of slavery and was ambivalent on the question of equality) began. In New England particularly, many free soilers were abolitionists at heart; in the mid-Atlantic states and even more in the old Northwest, political abolitionists tended to submerge their abolitionist identity in the broader but shallower stream of free soil." (James M. McPherson, "The Abolitionist Legacy: From Reconstruction to the NAACP", Princeton Univ Press, 1975. ISBN 0-691-04637-9.)

"History of abolition in the United States" in "Abolitionism", Wikipedia : http://en.wikipedia.org/wiki/Abolitionism#United_States

Answer 2

Many preferred gradual emancipation so that newly freed people could be absorbed into the free population in a sustainable manner.

Immediate emancipation of the entire slave population, they feared, would mean the instant creation of an unemployed, homeless population with few skills beyond agriculture and no place to practice their skills. These people would be free of the bonds of slavery, but would also and simultaneously be without the food and shelter (however substandard) provided by their former "owners".