Good, balanced article about the situation here. One way to look at it is northerners keeping the southerners down. Another way is private business and their ability to set their own rates being interfered with by FDR and his Interstate Commerce Commission
A third way is to recognize that a free market doesn’t exist when there is a monopoly supplier of an essential service.
One railroad into a town, that town has no other way to ship its products. In the days before interstates and long-distance trucking, that is.
So difference in freight rates often reflected more whether there was more than one railroad into a town than the costs of shipping from that town. Differential rates between north and south may simply have reflected the larger number of southern communities served by only one railroad rather than a conspiracy to keep the South impoverished and make the North wealthy.
The owners of railroads, after all, are simply interested in making themselves wealthy, not their region.