All of this misses the fact that slavery was central to the Souths economy.
And, therefore, to the North.
And absolutely critical to the economy of New York and Washington D.C.
You keep leaving out that part because it doesn't fit your narrative.
In 1860, Slavery accounted for 3/4ths of all cargo carried by the New England New York shipping industry.
They fought that war to get that money back, not to abolish the source of that money.
In other words, they were more evil than the slave holders. Their god was Mammon.