True. However, the problem is: doing that will land a government in a world of trouble.
Firstly, the popular unrest. While in my country, it seems that most people under 30 don't believe the government pension scheme will survive to our retirement, people older than that do hope for their promised pension. After all, that's what they worked so hard and paid so many taxes for. Pull the rug out from under them, and my bet is you'll have riots in the streets[0].
Secondly, loss of trust. Kill off something as big as a pension scheme, and good luck in convincing next few generations to believe you if you want to reinstate it again.
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[0] - Related - many young people will join too. While I fully intend to support my mother in her old age, if the government decides to take away her retirement money, I'd be pissed personally too - after all, they'll be impacting my finances as well.
Also related: that's why the loss of low-skill jobs by automation can't be ignored by people with high-skill jobs. Because after all, when your father, uncle, sister and closest friends will find themselves unemployed, who will they ask for help?