The South did not invent slavery, nor did invent slavery trade. In fact, the Southern United States had a minimal amount of slaves in comparison to other nations that owned slaves.
What do you suggest the Southern slave-owners pay their "workers" with? I hate to tell you, but the money trail led northward, not the otherway around. Let's not also forget that slavery was not illegal--even in the North. Northern people hated blacks just as much as Southern people did. They may not have wanted them to be slaves, but they surely intended on keeping them separate.
Once again, The Civil War was fought over states-rights, not slavery. Slavery was an underlying issue. It's funny that neither country went to war until the North failed to leave southern lands after the South seceded.
The money trail leading northward was more of a product of the Civil War. Wade Hampton of South Carolina was the country's richest men in ante-bellum America. In fact, plantation owners were most of the richest men in the nation. The poorer Southerners did not own slaves, so the actual slave owners did, in general, have the money to pay the slaves.
Secondly, slavery was illegal in the North by the time of thew Civil War. The constitution does not make slavery a legal institution in the national sense as you semm to think. Rather it does not comment on the legality of slavery thus leaving it to the states per the 10th amendment. In the North, slavery was either completely gone by the Civil War, or gradual emancipation had left but a few.
It is also a gross generalization to say that Northerners hated blacks as much as Southerners did. How do you account for the abolitionists, or the men in the burnt over district of New York who actually raided jails to free runaway slaves?
The North was too heterogeneous about blacks and slavery to say anything. The South in contrast was almost entirely homogeneous in supporting slavery, and those who didn't often moved North.