it's perfectly reasonable to worry about how the US is ever going to manage to pay for stuff it needs/wants. But accusing the Social Security Trust Fund of being a mere accounting fiction does not 1) do much to explain, analytically, why the budget is tight; 2) provide any justification for dealing with budget tightness by cutting Social Security, rather than some other thing, or by raising taxes. (It could well be that the optimum way of dealing with budget problems it to cut back Social Security in some way, but to talk yourself into this on the vaguely moralistic grounds that mere accounting trickery should be regarded as non-binding is quite confused.)
The U.S. budget is not "tight." It is unsustainable. It is a lie. Politicians have made a set of future promises that under the most commonly-believed economic scenarios cannot be kept.
Many people wrongly believe that this unsustainability is solely a matter of health care spending. That might have been true a few years ago, when it looked like the ratio of debt to GDP was not going to reach dangerous territory until at least 2040. However, now that there is a large risk of insolvency within twenty years, the demographics of the baby boom are also a significant factor.
The moral difference between accumulating real assets in a trust fund and accumulating IOU's is that real assets could be used to balance the excess of consumers relative to workers that the baby boom retirement will entail. If we had planted fruit trees, we would have more fruit to handle the increase in the dependency ratio.
Relative to a path with more fruit trees, somebody will have to consume less as the baby boomers retire. Either the younger generation will pay more in taxes, giving them less consumption opportunities. Or the older generation will have less in benefits. Or some other government service will be cut to fund the benefits, in which case the generational impact depends on what gets cut (if it's Medicare, the old folks have to pay for more of their own health care and get to consume less other stuff; if it's everything else, it's probably mostly non-elderly that get to consume less.)
Without the institution of Social Security, households would have acquired more real assets. They would have had both more means and more incentive to do so. Those who did not have the means or did not respond to the incentive would be dependent on the charitable inclinations of the rest in order to be comfortable in their old age.
To individuals, Social Security might seem like part of the solution for saving for retirement. For society as a whole, it is part of the problem. When one points this out, one is accused of wanting the elderly to suffer. On the contrary, I want to minimize suffering. To do be able to do that, we need to look at Social Security dispassionately and to assess its costs honestly. I do not think that the Trust Fund is of any use in promoting that discussion.