> If pensions were funded by actual retirement accounts, where employees invested money into some state fund and have it paid out for retirement this would be entirely unproblematic.

You're talking about a system of pension by capitalization, like in US, which comes with its own problems.

Namely that if you reach retirement age during a crash like in 2008, you're screwed. You have to work 5 more years hoping the market recovers in the meantime, or retire anyway and get way less than you put in.