Except that is politically expedient to always under represent the costs to properly finance those future benefits (eg by making rosy expectations of growth, or

Except that is politically expedient to always under represent the costs to properly finance those future benefits (eg by making rosy expectations of growth, or pessimistic assumptions about expected lifetimes). Those invalid assumptions can remain untested long enough for the relevant senior people and politicians to retire and now it is someone else's problem. The someone else is always the following generation, as they are the one voice without a vote when these decisions are made. So yes, it is always option 3.