Exactly. Pension systems where generation i+1 pays for generation i are fundamentally broken. If the population size sinks, generation i+1 will pay more. If pay

Exactly. Pension systems where generation i+1 pays for generation i are fundamentally broken. If the population size sinks, generation i+1 will pay more. If paying more and thus having less disposable income makes them defer having babies, you have your bad feedback loop right there. A better and stable system is where generation i pays for generation i.