In order to reason out (with help, not "argument for the sake of argument") this phenomenon measured in this migratory way I think it is important to explain what is known as free market forces.
Those who are free to choose better from worse do so and precisely as it is in their power to do so. Slaves will runaway from slavery. Slave masters will run away from defenders of slaves, so the slave masters will run to places where they can get away with slavery.
Where the slaves are free from slavery that place is a free market place in the sense that slaves are in command of the power they need to be free to choose not to be a slave.
Where the slave masters are free to enslave people, on the other hand, that is the end of free markets, as the slaves are no longer empowered to be able to choose to live in a place where runaway slaves are effectively defended against enslavement by the slave traders.
This was not unknown when this place was once federated as a number of people in a number of states, as explained here:
Reclaiming the American Revolution The Kentucky and Virginia Resolutions and Their Legacy William Watkins 9781403963031 Amazon.com Books
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Second, federalism permits the states to operate as laboratories of democracy-to experiment with various policies and Programs. For example, if Tennessee wanted to provide a state-run health system for its citizens, the other 49 states could observe the effects of this venture on Tennessee's economy, the quality of care provided, and the overall cost of health care. If the plan proved to be efficacious other states might choose to emulate it, or adopt a plan taking into account any problems surfacing in Tennessee. If the plan proved to be a disastrous intervention, the other 49 could decide to leave the provision of medical care to the private sector. With national plans and programs, the national officials simply roll the dice for all 284 million people of the United States and hope they get things right.
Experimentation in policymaking also encourages a healthy competition among units of government and allows the people to vote with their feet should they find a law of policy detrimental to their interests. Using again the state-run health system as an example, if a citizen of Tennessee was unhappy with Tennessee's meddling with the provisions of health care, the citizen could move to a neighboring state. Reallocation to a state like North Carolina, with a similar culture and climate, would not be a dramatic shift and would be a viable option. Moreover, if enough citizens exercised this option, Tennessee would be pressured to abandon its foray into socialized medicine, or else lose much of its tax base. To escape a national health system, a citizen would have to emigrate to a foreign country, an option far less appealing and less likely to be exercised than moving to a neighboring state. Without competition from other units of government, the national government would have much less incentive than Tennessee would to modify the objectionable policy. Clearly, the absence of experimentation and competition hampers the creation of effective programs and makes the modification of failed national programs less likely.
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So long as people are effectively defending slaves from slavery in one area (blue at one time was so called "conservative" by the way, and red was once "communist") so long will there be a sanctuary for runaway slaves, in that blue, or that red, area. So long as slave traders are defending their power to enslave their slaves, in a red area, or a blue area, so long will there be a place for slave traders to go and be free from any moral defense against such crimes.
"Net tax payers migrate out of Blue states and into Red states."
Is it a tax, really, or is it an extortion payment? If someone must expend all the costs required to run away from involuntary taxation (extortion) then that is itself an added "tax" added to any other "taxes" already paid to those enforcing such extortion.
As to how rapid will slaves runaway from slavery when it is in their power to do so?
If the structure of the federation is false then the slave masters run the whole show, and they take the lion's share of the productive capacity of the slaves; while the lesser slave masters at the false "State" level, or the false "City" level, or the false "Corporation" level, are left fighting each other over the remaining crumbs.
That is simple to quantify with a simple comparison between the extortion racket known as the IRS, and the other extortion racket known as the state liabilities. The obvious measure of who is the boss of who is clearly marked.
What happens if one of the states, or several of the states, outlaw all forms of slavery, and those people in those states welcome runaway slaves whose only duty in that federation is to participate in due process, which is jury duty, or in case of invasion by an aggressive military force perpetrating war of aggression, it is the duty of free people to do what they can to defend against such crimes.
If that is not a familiar theme, then the slaves will not find sanctuary from slave masters in blue or red states. Arranging the chairs on the Titanic comes to mind, or game theory, as explained through something called the prisoner's dilemma also comes to mind. The migration is perpetual as the severity of the "business cycle" forcing migration fluctuates from feast (boom) to famine (bust), here, then there, then here again.