First, please note that the vast majority of Northerners did not detest slavery in the South. They didn't want slavery in the territories (because they wanted that land for white settlers), but they didn't really care that much about black people. This was especially true in the early years of the abolitionist movement. Northern whites did not,as a rule, mind having slavery exist in the South and did not want a whole bunch of freed slaves coming North to compete with them for jobs and to, perhaps, live near them.
Even among those Northerners who truly did detest slavery, there was not complete support for abolitionism. One reason for that was that the Constitution allowed slavery. To embrace abolitionism, then, was to say that Southern slave owners should have their legal property taken away from them. Another reason is that the abolitionists were the most radical part of Northern society with regard to this issue. People rarely support extreme points of view in large numbers.
So, in answer to this, I would point first to the fact that most Northerners did not hate slavery as much as this question implies. Second, I would note that slavery was an embedded part of American society that had been around forever and was sanctioned by law.
It should be considered that while many in the North may have hated the immoratlity of slavery, they were more interested in protecting their economic interest Seldon (2011). Southerners who did business with Northerners threatened to boycott them if something was not done to curb the enthusiasm for the abolition of slavery. Some northern business people responded to southern wishes.
Also, it was probably abhorrent to some that the abolitionist in action in not also in word were indicating that slaves (Blacks) were human beings and worthy of social equality with Whites (Seldon, 2011). This radical social agenda during this time did not sit well with the ingrained mindset of segregation of the races.
Seldon, H. (2011). A moment in abolition history. The Liberator Press, 1831-1865. Retrieved from http://www.theliberatorfiles.com/a-moment-in-abolition-history/