This is an interesting and oft-repeated theory, but for at least the last three decades, if not longer, the examples of the most recent states the "liberal locusts" have just destroyed when it gets trotted out have always been some combination of New York, California, and Massachussets, and the implication has always been that they are next moving to previously "pure" states in the South or inland West.

If the trend was really as claimed, you'd expect their to be a trail of states to point to that have been moved through over time, rather than always the same states.