Updated: Mar 7, 2022
One reason why a Keynesian-style boom-bust economy is needed is that it allows market directors to buy/sell at mathematically predictable times.
Let's say you want to legally steal land from the proletariat. You can lower interest rates and glorify leverage. Sell credit cards. Encourage people to take out loans to pay for college, cars, houses, etc. A rising economy would attract investments. The investments would drive the market further up, attracting even more investments. The goal is to heat the market far beyond it can organically support. Suppress any news about a potential crash until it is due. Sell assets for liquid cash before the crash. Then, allow news about the crash to come out. You suddenly have an illiquid market. Part of it has become insolvent. People would be forced to sell away their non-liquid assets (hard assets). Since you have piled up cash, shop around for cheap property. Financially distressed families and businesses are good targets.
If you had sound money with no central bank, you simply wouldn't be able to design the market the way you want. You wouldn't be able to manipulate interest rates. Without centralized control, there simply wouldn't be enough variations in overall output.
Ideally, output increases linearly with time. Thus, the curve is a straight line. Whatever variations occur would be less predictable, like one caused by a drought or a bunch of tornadoes. None of these variations you would be able to centrally direct and plan. Without planned boom and bust cycles, you wouldn't be able to siphon off the market's aggregate output.
Thus, you shouldn't have sound money. And you definitely need a central bank, unless you want to work.