A reminder to everyone: Social Security is NOT a retirement plan, it is an insurance plan. When your 401(k) is cratered by the stock market or your pension goes the way of Enron, SS is supposed to be there to hopefully keep you from being dumped in the gutter. Tying SS to the stock market would not be a smart move.

You're drawing a semantic distinction that doesn't really exist. Insurance for retirement, retirement funding -- it's all the same thing.

A 100% equities (or 100% Enron) portfolio is not the only or best option available to the SSA. And the SS portfolio can't be panic-sold by the individual retiree in a market downswing. Using equities to achieve some additional upside for SS in one way or another is plausibly a reasonable idea.