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.