Madoff and Social Security

What makes the Madoff scandal any more scandalous than the current Social Security ponzi scheme we have in the US? A Ponzi scheme is where you promise a return on invested money and instead of investing it, you spend it. Later you take money from "new" investors to pay the old investors so that no one will be suspicious. This is what Madoff has done. He took billions of dollars in return for a promise to invest the money. He showed good returns to his victims for several years but the returns were phony. He was using the newly invested money from new investors to pay the old investors and on and on it went until the whole thing imploded as they always do.

Social Security in the US is nothing more than a Ponzi scheme writ large. The Federal Government took our money in return for a promise to pay. However instead of investing the money they have spent it and issued IOU's to the Social Security trust fund. They are using tax reciepts of current workers to pay the retirement benefits of the older workers. Outside of the ability to tax the workforce, what makes the Social Security system any better than Madoff's Ponzi Scheme?