Because central banks can flaw the true nature of bitcoin, besides that also makes it easier for the government to carry out suppression/intimidation against the people involved, for example by making unilateral regulations, enforcing taxes and so on, which in essence might hurt especially for investors. IMO, bitcoin will be better if it runs without the Central Bank so bitcoin can move more freely. And what bitcoin needs is the presence of cold hands from the government to help and oversee its development, so that the positive benefits of bitcoin become more focused.
Bitcoin already runs without a central bank. There's no single entity in charge of the issuance of new coins or the total supply of the cryptocurrency. Anybody can contribute to its development, meaning that Bitcoin is a free (free as in freedom) cryptocurrency for anyone around the world. In the case of central banks, we still depend on them because they serve as gateways between Fiat and Crypto. Also, many merchants and businesses accept Fiat at a greater level than Bitcoin.
Because Fiat is still largely used in many regions of the world (whenever it's USD, RUB, EUR, etc), we need to interact with a bank one way or another. Credit/Debit cards are all dependent on banks, unfortunately. However, if cryptocurrencies were to become the only medium of exchange (which is highly unlikely), then there would be no need for central banks as we can be our own bank. After all, Bitcoin was designed from the ground up to eliminate the middleman. Therefore, this enables us to store and interact with our Bitcoin without the need to trust a third party (central bank or government) at all. Just my thoughts
