Sure, if you're starting on that basis. But it's a different thing entirely if you start out with an explicit deal saying "you pay 30% of your income to the government, and you get a pension when you retire" and then after you fulfill your part of the bargain, the government says "oh uh, that money you paid, we spent it."

We now have mandatory superannuation contributions which work pretty much how you're suggesting, and the government is pushing towards getting rid of pensions in future.