Anyone with a calculator and a knowledge of 8th grade mathematics can see that it's not possible in the long term for an investment strategy to exceed the overall growth rate of the economy. Only a moron would expect to get 8% returns forever if the economy is growing at 3%-4% because if your investment fund is growing exponentially at a rate greater than the economy as a whole after a certain number of years your fund would need to own more than 100% of the economy.
What happened is that a bunch of public sector pension funds got lucky in the 1990s and experienced about 8% returns for a few years. This was a fluke but they got greedy and wrote into law that the pension fund must achieve those returns every year forever, as if legislating investment returns magically causes economic growth to appear. All these pension funds are now insolvent and the people depending on those unsustainable promises are going to get increasing desperate and hostile as the mathematical reality inevitably closes in.
I agree. The point is that they can't get a decent return so government debt is not a problem. Its free money IF you can find a place to invest it. Better than free - atm government debt has a negative rate of return.