Search for the funding status of defined benefit pensions for most government entities. Most are counting on passing on the buck to future generations to fund their promises, either via increasing taxes or decreasing the value of money.
It doesn't exactly matter if you personally paid for your pension or the state took some percentage from you paycheck or any other imaginable system, if in 40 years you want to retire and the majority of society is made up of other retirees, any form of currency isn't going to be worth anything.
No matter which way you turn it the sustainability of a retiree lifestyle hinges on a large part of society showing up at work on 9am. In 40 years, that's not going to be your peers, it's whatever children your generation produced. If you don't want to pay for benefits that ensure enough workers will be around then you are betting that we got rid of human workers in 40 years of time or investing your money into a hut in Alaska and some shotgun ammunition.