There is a bad and good side of legalizing Bitcoin. The negative effect will justify your statement. It can only lead to Bitcoin being centralized because of the government's control. The positive side is that it may also lead Bitcoin into a much stable economy. In which the bitcoin users can decide whether they will be supporting it or not and should accept the outcome.
So, there is nothing legalizing bitcoin is really going to change except for the fact that if you are making use of an exchange in conversion to fiat, then the tax law is applicable to you and until bitcoin can be used without having to convert to fiat, we just have to accept that and even without legalization, some countries are already doing that anyway.