Goodness me, I thought your point was that several "loyal" slave states not only substantially increased the number of free blacks in the old union but assured their better treatment.
No, but that's a good thought for an author to investigate. The correlation between slaves per capita and secession shows that the states most invested in slavery seceded first. Perhaps the loyal slave states did treat free blacks better than the disloyal slave states. Since the disloyal slave states were obviously more committed to white supremacy, it's possible that the loyal slave states treated free blacks better.
I don't know that anybody has established that life for free blacks was "better" in the North or South, depending on the definition of better.
In his book
Slaves Without Masters: the Free Negro in the Antebellum South, Ira Berlin says
Far more than restrictive regulations, the free Negroes' precarious, often impoverished situation anchored them to their homes and made them reluctant to emigrate. Ties of home and kin, their reputation with white customers or employers, their familiar daily routine, and their knowledge of the countryside often provided the only security for free Negroes hand in a society that was hostile to their very existence. Fears that these ties might be sundered frightened many blacks; for them any change could only be for the worse.
For many free blacks, living in the North might have an improvement. But things like poverty, their desire to stay close to family, etc, "anchored" them to the homes, they couldn't leave even if they wanted to. They didn't have the freedoms, resources, and opportunities that we take for granted today when it comes to deciding to move.
There was a quality of life advantage that has been acknowledged for Northern free blacks: the ability to engage in free speech. As noted by Berlin,
Still, free Negroes enjoyed a degree of liberty and self-expression unknown in the slaveholding states. The host of black newspapers, the activities of black abolitionists, organized churches, schools, and conventions, all spoke to the differences between the North and the South. No matter how successful a black tradesmen might be in the south, he never dared raise his voice against racial oppression. Although omnipresent racism made a mockery of many of the legal rights of Northern blacks, Southern free blacks who moved North generally found a measure of liberty altogether absent in the slave states.
I recall one scholar say that free Northern blacks were basically the spokesmen for free and enslaved African Americans in the USA. For free blacks and the enslaved, free speech was stifled in the South.
Of course, even whites were limited in what they could say about race. Consider the case of native born southerner Hinton Helper,
from Wiki:
Hinton Rowan Helper (December 27, 1829 – March 9, 1909) was an
American Southern critic of
slavery during the 1850s. In 1857, he published a book which he dedicated to the "nonslaveholding whites" of the South.
The Impending Crisis of the South, written partly in North Carolina but published when the author was in the
North, argued that slavery hurt the economic prospects of non-slaveholders, and was an impediment to the growth of the entire region of the
South.
Anger over his book due to the belief he was acting as an agent of the North attempting to split Southerners along class lines led to Southern denunciations of 'Helperism'.
(The book) generated a furor in the South, where authorities banned its possession and distribution and burned copies that could be seized.
- Alan
