They will only have more money to spend with. Let's just admit it that only few of the government in the world are transparent. Some are very opaque to the point that they have a lot of money but the people are still blinded with their statue. If they put tax just to legalize the crypto, well, I can say that the crypto world would weaken because of them.
I think that a government runs on the taxes that we pay to them. But it is also right to say that once they will impose tax on bitcoin I think that then they will manipulate the system and will increase the tax amount from time to time which will not be in favor of the investors and bitcoin holders.