Keeping retired people alive requires devoting some proportion of current economic output to their welfare. Whether that proportion is paid from private savings, public savings, or current taxation ultimately doesn't change the fact that it comes out of current production. You can't save (nice) food, health workers, winter heating, etc.

So the real fight is what proportion of current output goes to old people. Private schemes try to ensure wealthy old people get the biggest slice. Public schemes are more vote driven. It doesn't make them Ponzi schemes.

Social Security is running a ~$2.79 trillion dollar 'surplus' as they have collected more than they have paid out. Which means they have not been paying out 1:1 with money paid in.

It's also not just a pension fund as you can receive benefits well before 62. Death of spouse with under age children or permanent disability.

Now, this does not mean it's a great or even a good investment. But, the trade off of safety vs returns is not actually that bad assuming you live longer than average.

PS: Another way of looking at it is there are no 100% safe approaches to investing 10's of trillions of dollars. Your stuck leveraging GDP growth which is only slightly better than inflation and frankly that's what SS does.