This is a point I often try to get through to the "it was all about slavery" crowd.
They want to believe the hatred for slavery stems from the moral outrage of forcing people to work without pay.
The truth is that the hatred for slavery comes from a hatred for black people, and a hatred of "scabs" who would undercut the wages of white people.
For the VAST MAJORITY of the people in the North at that time, it wasn't "forced servitude" which was hated, it was black people and labor competition.
It wasn't about morality, it was about their own prejudices and selfish interests.
Only a handful of liberal nuts, mostly in Massachusetts, hated slavery because they saw it as immoral. The rest of the nation hated it because it brought black people into their lives, and they feared labor competition.
Bingo. The PC Revisionists are desperate to prop up this image of the North as being champions of equality and civil liberty. They were anything but. Massive racism was the NORM everywhere around the world in the mid 19th century. Read those statements by Lincoln. He got elected. That alone should tell you how widespread those sentiments were.
Abolitionist newspaper baron Horace Greeley put it succinctly: "the Republican Party's stance is "all the unoccupied territory shall be preserved for the benefit of the white caucasian race -a thing which cannot be but by the exclusion of slavery."
They certainly did not love Black people. If anything, they hated Blacks far more than Southerners did. The corporate lobbyists wanted to keep slavery out of the territories because they wanted more votes in the Senate to pass their tariff/government pork legislation. The ordinary White working class wanted to keep slavery out of the territories (and the Northern states) because they wanted it for themselves.....certainly not out of any sympathy for Blacks. Kansas and Oregon's first constitutions didn't just ban slavery. They banned BLACKS!
First Point: De Tocqueville's visit to the USA came in 1831, decades before slavery became the existential political issue it was in 1860.
So, his comments then do not necessarily reflect realities of 1860.
Second Great Awakening c. 1850:
Second Point: The vast majority of Northerners in small towns and rural communities never saw African Americans, so they didn't hate blacks, they didn't fear blacks, they didn't know any blacks.
The issue of slavery for them was strictly theoretical -- did slavery comport with the Declaration of Independence claims that "all men are created equal and endowed by their Creator with certain inalienable rights"?
The answer was: No!
Third Point: The religious Second and Third Great Awakenings (1790-1860) progressively added to Northern awareness of slavery's sinfulness.
So Northern moral anti-slavery sentiments -- which had barely touched the South in de Tocqueville's time (1831) -- by 1860 had grown louder and more insistent.
Fourth Point: After de Tocqueville's time (1831), the Southern Slave Power became steadily more blatant and aggressive, as illustrated in the US Congress's Gag Rule from 1836-1844, under which Congress was forbidden from debating slavery at all.
For another example, the 1850 Compromise required the Federal government to enforce Fugitive Slave Laws, regardless of states rights claimed by abolitionist states.
Fifth Point: Slave Power challenges to the authority of Congress -- to make slavery illegal in US territories -- combined with the 1857 Dred Scott SCOTUS ruling, together overturned the Founders' basic understandings about the Federal government's role in setting slavery laws.
Finally, in de Tocqueville's time, where Southern whites & blacks worked together, it was always as dominant slaveholders over their submissive slaves.
In the North, whites could not legally dominate, but they could force freed blacks to work for lower wages, and therefore at jobs whites didn't do.
Bottom line: during the antebellum period, there were no Northern freed blacks who migrated South to live in slavery, regardless of how difficult Northern life might be.
Throughout this period there were rapidly growing freed-black populations in Northern states, notably in the very states subject to so-called "black code" type laws.