SS and FICA are very regressive. It's interesting that the lowest rates roughly correspond with the median income - as if the rates were tailored to get the lowest rates to the majority of the voters, while screwing (relatively) much smaller groups at the ends of the scale.
It's not so much regressive as it is "supposed" to be a penion insurance plan separate from the rest of your taxes. There is a cap on benefits, so there's a cap on what you contribute to it, not unlike the cap on contributions to a 401(k) or IRA.
Of course, we never got our lockbox so the upcoming generation of retirees elected governments that spent that retirement money on other stuff now wants to raise taxes so that the current young folks can pay for their irresponsibility.
