Bitcoin can improve countries economy because it will help a lot of people to earn money and the people will use those money to spend on the things that they want and those profit of the shop or the store that the people used to buy things with. Then it will boost the shop or the store's income and the tax of that store will go up too and it will help the country to have a better income which will help itself to improve its system and economy.
Nice explanation. Basically as more money comes to the country, the better it economy becomes. Regardless of in which form it is. Bitcoin is still money. On the other hand, because bitcoin transactions are not really taxed, as more bitcoin users a country has, the tendency to have lesser tax accumulated is increasing. Imagine a country where a good percentage of people are using bitcoin in most of their transactions. It will leave the country poor in such a way that the government can't do anything about the tax thing. They can't increase the tax on fiat because that will just make more people choose to use bitcoin. On the other hand, there is no possible way that they are able to ban bitcoin unless they remove the Internet access in their country.