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.