Modest rise in taxes... Across the board to person in the United States? To only the 50% of people who are taxpayers? To only the top 10% who pay 70% of the taxes already? Tax those who do not generate income traditionally but rather earn based on investments? Seizure of personal assets?
Depending on how you go about this, you could create economic stagnation because of burdensome pension programs.
Alternatively, you could cut benefits, or privatize the investments rather than simple redistribution from one payroll tax payer to one pensioner.
I'm in favor of privatization combined with benefit reduction and increased minimum retirement age.
The combination of these three could easily solve any pension shortfall and generate long term wealth for every American.
These scare stories are solved by a modest rise in taxes. The obligations are summed over many decades and projected into the future.