"I guess you’re right on the economics, but those taxes were never a problem of economics. They were politics all the way through. We put those payroll contributions there so as to give the contributors a legal, moral, and political right to collect their pensions and their unemployment benefits. With those taxes in there, no damn politician can ever scrap my Social Security program."**
Krugman knows he is full of blarney (trying to keep it clean). And FDR knew he was creating a system that would be impossible, politically, to fix. It was established to create a political class of citizens who would then be beholden to and dependent upon, the federal government. The workers will feel trapped into continued support because of the money already taken from them and "invested" into the system.