Never said that. Said they believed different things.
I highly doubt that ANYONE -- North or South -- "insisted blacks be forever enslaved for the benefit of their white masters."
Then you just aren't very familiar with the period. In 1800 the consensus, South and North, was that slavery was a bad thing, but nobody knew how to get rid of it safely.
By 1860 most in the North still believed this, but in the South a new consensus had emerged, that slavery of the black man to the white man was the natural order of things, and therefore a positive good.
The new veep of the CSA made an impromptu speech shortly after his election, that as far as I've ever been able to find out was received with unanimous acclaim throughout the South.
" Our new Government is founded upon exactly the opposite ideas; its foundations are laid, its cornerstone rests, upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and moral condition."
http://www.fordham.edu/halsall/mod/1861stephens.asp
I have by no means taken Mr. Stephens out of context. If you like I can find dozens or hundreds of similar quotes that show the South had developeda consensus that slavery was a positive good that should be extended indefinitely both in time and space.
What you’ve posted is very much in line with the secession documents of all of the States. The Confederacy wasn’t about State liberty, they were very narrow focused on a few issues and were very much anti-individual liberty. They didn’t give a rat’s ass about the 10th amendment or Constitutional values. They were even willing to set up a new monocrachy (and for anyone who doesn’t believe this, read the articles of secession by each state).
“Our new Government is founded upon exactly the opposite ideas; its foundations are laid, its cornerstone rests, upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and moral condition.”
I would argue that the one thing different about the majority of northerners from that statement is one word: slavery. Take that word out and you’ve described the beliefs of most northerners. Keep in mind, too, that slavery was practiced by black Africans, so the one sliver of difference communicated here is a sense of white supremacy...a part which yankees, by in large, accepted as well.