I do not want to be side-tracked into a long debate about the virtues of having a central bank, beyond simply observing that for all practical purposes we either have our own central bank, as the great majority of countries do, or we abandon our own currency and use the services of some other central bank, such as Hong Kong and Argentina effectively do (they use the services of the US central bank of course).
As long as we want to retain our own money, we need to have a monetary policy, and some institutional structure with which to implement that monetary policy. The key issue is what that institution, typically a central bank, should try to achieve with its powers.