You do a terrible disservice to the very strong abolitionist movement in the pre-civil war North. Look it up on google. It was one of the principal movements that supported the war as a war to end slavery.
That said, not all northerners were primarily motivated to ending slavery.
What unified the North to fight secession was geopolitics. Control of the Mississippi river system to the gulf was extraordinarily valuable and divided nations controlling one part or another would have brought European powers into CONUS and endless trouble.
Ohio and Illinois and the rest of the midwestern breadbasket and industrial plant would have had lost inexpensive access to world markets should another nation control New Orleans.
But there were plenty of powerful northerners who did not want to win the war or eliminate slavery (See Gen. McClellan, who ran the Army of the Potomac for years.)
Your cheap labor argument doesn’t hold much water, imo.
Yeah. Google, they're very good on political issues.
Better you should get your hands on Northern Editorials on Secession. It's about 1100 pages split into two volumes. 495 editorials, selected from 190 different newspapers over a period of ten months beginning in the Fall of 1860, are included. I would estimate than not more than 15% concern themselves directly with slavery and/or Negroes. Of those at least several support Southern Slavery, and still some others are neutral.
A quote from the introduction:
The issues of the campaign [of 1860] were confused. The status of slavery in the territories, supposedly the dominant issue, was subject to the fortunes of the election but also the actions of the Supreme Court. {Emphasis added. I.e. Slavery per se was not the dominant issue.]ML/NJ