Market regulation gives users the legal support even if something go negative. In particular if a scam approach or a cheating took place with the name of cryptocurrency it can be taken to further investigation to the government. This takes off unwanted fear of common people who hesitate to get into cryptocurrency usage for these reasons.
How are you going to control the decentralized system? This is contrary to each other. And even if it is possible, then what is the meaning of cryptocurrency at all, if not freedom?