The IAMNPP argument takes a different slant if there was a market meltdown that causes a large decrease in someone's portfolio.
If anything NYer, a market meltdown would make the IAMNPP even MORE distasteful.
The IAMNPP is invested in, wait for it, the Market.
It would be in even worse shape than it is now and would likely immediately have to cut Benefits Again.
The members in it would have Zero say in how their money was invested.
The members in it would not be able to move their money to investments of their choice, they would be left to the will of the folks running the fund, and I have to say, I'm not impressed with their lineup of financial "experts".
A market meltdown would be the absolute worst thing for anyone currently in the IAMNPP.
However, if you have a 401K, you have the freedom to invest however aggressively or conservatively you choose to at any time.