The sad thing that just the two parameters basic income and flat tax rate are flexible enough for a wide variety of policies. Want scandinavian style socialism

The sad thing that just the two parameters basic income and flat tax rate are flexible enough for a wide variety of policies. Want scandinavian style socialism: set the basic income very high and have a high flat tax rate of maybe 50%. Want a more individualist approach: set basic income to the bare necessities and set the flat tax rate to 25%. Want to borrow to fight against a recession, keynesian style: increase basic income without raising flat tax rate. Want to save for bad times: increase flat tax rate without raising basic income... I guess this kind of system can only emerge due to some drastic change or historical accident. E.g. the eastern european countries have a flat tax system because after the collapse of the soviet union there was no complex incumbent system in place. I would love to know if there is a way to get to such a system using the normal democratic process. But if it exists, I don't see it.