I think the fact that railroads came out of the northeast had more to do with the concentration of capital than the focus of government. I think that the end of slavery up north had more to do with population than any noble motive.
You have a population of poor people clamoring for jobs and it costs less to pay them nothing and shift for themselves than it does to maintain a slave. Simultaneously the lack of poor people demanding to work for free kept the south agrarian and slave based. Who cared about air conditioning? Poor folks are expendable if you have enough of them.
Id bet if you compared mortality rates among slave and free factory workers the slaves come out ahead. Because you bought slaves, paid cash money, and free poor folks are free.