Paul Ryan is catching grief for his proposal to convert Medicare from "all the medical care you wish to consume" to grants of $X per year. This seems unimaginable to people (forgetting for a moment that the US functioned for nearly 200 years without it at all).
But what if Social Security were Medicare. What if, instead of giving $X per year, Social Security made an open-ended promise to fund whatever consumption one thought necessary to maintain his or her lifestyle. Can you imagine the fiscal disaster? The horrible incentives
And if Social Security had been structured that way, and we were now trying to change it to fixed grants, what would people be saying? They would say, "what if something unexpected happens - won't that just leave people in the cold?"