What was the rationale of allowing high-wage earners to pay proportionally less relative to earnings than the middle/lower class? IF the common refrain that high earners should pay more taxes, then why have a payroll tax cap that allows these same earners to pay disproportionally less relative to their earnings?
I cannot answer historically but the payroll cap is on social security and also effectively caps benefits since social security benefits are derived from the amount you paid in while you were working. Note that Medicare isn't capped.