Isn't that definition of a ponzi scheme?
http://www.investopedia.com/terms/p/ponzischeme.asp
That perfectly describes what happened to the Teamster pension fund. The fund is collapsing because there is a lack of new workers. The pension worked beautifully as long as there were more workers than retirees. Once that starts to reverse, the fund collapses.
First, I assume this means you admit that Social Security is nothing like a ponzi scheme?
As for the rest, you left out important parts of the definition, as Ponzi schemes involve fraud. Additionally, a Ponzi scheme requires a constant stream of new capital from investors while a pension does not. Not only do pensions gain additional capital from investments, unlike a Ponzi scheme, but there is absolutely no requirement for their liabilities to grow faster than their assets, also unlike a Ponzi scheme. The definition isn't just wrong, it's wildly wrong.
As for the Teamsters pension, it looks like the fund is at risk of failure for a number of reasons, not simply that they have fewer employees now.
But pensions still rely on more people paying in than taking out. If more people are taking out, the fund collapses because the fund is forced to liquidate its investments. It doesn't matter if the fund actually had investments or not since the end result is the same - a lack of new investors causes the fund to collapse. That mechanism of relying on new investors is what defines a ponzi scheme.
This is false. Pensions do not require more people paying in than taking out so long as they have properly structured their investment portfolio and their level of benefits.
When you have less money coming in than going out this does cause a pension to liquidate some investments, but that's not inherently a bad thing. Pensions do not need to grow ever larger in order to fulfill their purpose, much like your retirement account is not a failure if you are having net withdrawals later in your life.
This is why when looking at a pension's health people generally look at its assets as compared to its liabilities, not how many new workers they have coming in. It's also why a comparison to a ponzi scheme is absurd.
To be fair, the non-ponzi elements of pensions had realistic expectations when they were created. ZIRP and NIRP are recent problems. In 1990, you really could get 10% every year from bonds alone. I remember regular bank accounts paying 5% interest. That was a really glorious time for savers and retired people.
Most people get a very small percentage of their income from interest, so high rates didn't really mean shit for regular people almost ever. I'm sure that pension funds and other institutional investors could take advantage of them though.
That all speaks to the challenges of managing the fund though, which is a totally separate thing from calling them a Ponzi scheme, which is badly inaccurate.
