George, by and large, wages in the South are lower than in the North. Medicare (and SSA) taxes are a percentage of earnings. Hence wage earners from those states with lower wages would pay a lesser amount, though the percentages are the same. The awarding of SSA benefits is predicated upon gross earnings. A lower wage history would result in a lower award of SSA benefits.
To the extent fees paid to doctors are lower in the South, compensation from Medicare to those doctors would be lower than in the North, where fees are higher. This tends to balance out over time and section of the country.
An increase in these taxes applied only to the South would upset the rough balance now in effect, based upon the above statement, and again the South would suffer unduly. Here we go again! BOHICA! Stan