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.
First response: pathetic excuse making. Numerous other quotes as well as laws as well as votes show this was reflective of Northern attitudes about Blacks...1830, 1860. It hadn't changed.
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!
Second Response: This is simply false. Their own political leaders talked openly about how much their people disliked Blacks. For example, here is Ohio Senator John Sherman ""In the State where I live," said John Sherman, on April 2, 1862 "we do not like negroes. We do not disguise our dislike. As my friend from Indiana (Mr. Wright) said yesterday, 'The whole people of the Northwestern States, are, for reasons, whether correct or not, opposed to having many negroes among them, and that principle or prejudice has been engraved in the legislation of nearly all the Northwestern States." I already provided many more such contemporary quotes from Northern political leaders.
Then there is the matter of the various laws enacted with popular support to force blacks to pay a hefty bond to enter a state (Illinois) or the original constitutions of Kansas and Oregon forbidding Blacks from settling there, etc etc. The evidence is overwhelming.
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.
Third response: Northern anti slavery sentiments had grown so strong that abolitionists could not get more than single digit percentages of the vote anywhere in the North.
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.
Fourth response: Some rule. The expansion of slavery was certainly debated non stop at that time. The Southern states went from a position of equality to falling into the clear minority of states in the union over this time. So much for any supposed "slave power".
For another example, the 1850 Compromise required the Federal government to enforce Fugitive Slave Laws, regardless of states rights claimed by abolitionist states.
Relevance? That was part of the deal made in the Compromise of 1850. Northern politicians readily agreed to it.
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.
Fifth response: No they didn't. The ruling was that the federal government could not exclude American citizens from entering any US territory with their property. Note that we are talking about territories here and not states. They were not sovereign. States could exclude anything but transit to a slaveowner bringing his slaves there because states are sovereign.
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.
Finally.....Whites could not dominate in the North? What on earth do you think they did? Blacks got lower wages and that's if Whites did not riot to prevent them being hired or simply refuse en masse to work alongside them. Given Blacks were a small minority the boss was then faced with either firing the few Blacks or losing his entire workforce. Naturally they always chose to fire the few Blacks who they had employed. Blacks could not sign legally binding contracts nor serve as witnesses in court. If that's not Whites dominating, what is?
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.
Bottom line: Sure Blacks did not move to the South to live in slavery. Some certainly did to live as freedmen. Black populations did not grow rapidly in Northern states. The underground railroad ran to Canada for a reason and that reason was that Northern states did not want Blacks living there and made it as difficult as possible for them to do so.
Obviously the Northern population came to love blacks more in the intervening 30 years. That's why Illinois enacted the "Black codes", to show how much they loved black people.