I think you will find that the Social Security cash flow surplus essentially doesn't exist anymore. The latest published data, for 2011, showed it at less than 9%.
No one, including the SSA, is debating whether the program will cease to be "pay as you go" at some point, and that time is imminent. It's going to run a deficit. Permanently, structurally, as a matter of fact, unless taxes on our generation are increased and/or the program doesn't pay out what the previous generations promised themselves we would pay them.
What they refer to as "the accumulated surplus" is the Trust Fund. That's nothing but government bonds, which is all it ever could be (by law). The federal government took the money and spent it. In order to redeem that debt to pay SS benefits out of the Trust Fund, the federal government would therefore need to either:
1) Acquire additional revenue from the present working generation, more revenue than they currently are receiving (ie. increased taxes), or
2) Sell new debt under "the greater fool" theory, where they find investors willing to buy bonds to fund the redemption of the Trust Fund debt. This is nothing more sophisticated than a credit card balance transfer. The issue with this approach is that eventually the bond market will freak at our deficit size and/or our debt-to-GDP and then the government will be forced to default in one form or another.
From the SS program's standpoint, one major problem is the actuarial liability is increasing. People are living longer, which is great, except that means they will be drawing benefits longer if the retirement age is fixed. This is why the retirement age needs to increase to put it on par with the historical benefits. Yes, and that means the Boomers and all subsequent generations should work longer before they retire.
Furthermore, it's essential that the previous generation share the sacrifice: how is it fair that our (and future) generations will have to work longer than they did before we can retire, and pay higher taxes than they did, merely to pay them what they promised themselves? I think you'll find that every politician who talks about "fixing" Social Security adamantly adheres to the platform that the previous generation "deserves" the benefits exactly as they promised to themselves, but all future generations will just have to suck it up to bail that out while also facing later retirement and reduced benefits.
I am aware that "they" include my parents and your parents. However, "they" didn't fix anything during their time. Merely attempting to dilute responsibility among an entire society doesn't change the fact that the situation exists, is unjust, and needs to be fixed.
If I were to open a joint checking account with my elementary age child, deposit $10,000, spend that money on a new car for the household, then write a $10,000 post-dated check for 30 years from today "to cash out my original savings deposit", how is it my child's responsibility to make me whole just because I put her name on the account? Because that's what the previous generations did: they told themselves they were "saving" money in the Trust Fund, but they spent it all on general budget expenditures (albeit via one layer of notional, bookkeeping indirection called the Trust Fund).
Yes, perhaps one day I will live to be of retirement age. The reason I want us to break the vicious cycle is that I don't want to visit the ignominy of what our parents' and grandparents' generations did to us on *our* children and grandchildren.
People should stop counting on government pyramid schemes to fund their retirement. Our generation has a chance to start accepting responsibility to save money on our own and break the cycle. Yes, it's too late for the mathematically-challenged previous generations, so we can give them some means-tested welfare if they need it.
...but we don't *owe* them merely because they decided we should, before we were born. You'll notice I never suggested a "Logan's Run" approach to the problem, or sending the elderly off onto a an ice floe. However, the situation is unjust and if we, as a society, want to ensure that our parents and grandparents don't starve then it's important that we *all* sacrifice rather than just laying the bill at our generation's feet. It seems more fair that they should accept means testing and increased retirement age if we are going to have to pay in more than they did just to get less out someday (presuming *our* children don't just abolish the program entirely).
Oh, and yes, the USPS could conceivably be fiscally responsible, and technically they are currently doing so by budgeting for these massive liabilities. The problem is the federal government is absconding with their money and spending it on general budget expenditures, just like the erstwhile SS cashflow surplus. Also, as a previous poster commented, the USPS should ditch their pension and switch to a defined contribution plan (eg. 401(k) type)—that would certainly be fiscally responsible.
Finally, with respect to whether some theoretical Social Security Trust Fund that sequestered cash flow surpluses and then released it later (much like an enormous bank savings account) would destroy the currency or not, I think the answer is clear. We would have ended up in a very similar, unfortunate situation today had they done that. First, trillions of dollars would have been removed from circulation, which naturally would cause deflation; however, the Fed doesn't allow deflation, so they would have just started their Quantitative Easing programs decades earlier (ie. printing money to buy government bonds). This would have established a government bond-based "Trust Fund" on the balance sheet of the Fed, and the bond purchases would have funded general federal budget expenditures... just like happened in reality. Anyway, once the money was paid out from the "savings account" style Trust Fund, then inflation would hit our generation hard (not the previous generations as much because their SS benefits are tied to inflation already), thereby making our generation poorer. Same net effect as raising taxes on us.