just because some people don't pay their taxes when trading bitcoin and cryptocurrencies that doesn't mean bitcoin is affecting the economy of the whole country! these same people would never pay their taxes when they do other things so the economy didn't change because of them.
Well there could be indirectly form of effect that bitcoin plays like if you see how the marketcap volume for bitcoin in corresponding fiat value in dollars. It will took billions of dollars coming from around the world. So this money would be taken from the countries economy for bitcoin to add up its market cap volume. If not for bitcoin then these money would circulate in the countries economy and not in bitcoin.
One thing that is very clear to me and may be consider as direct impact of bitcoin on economy. I think that bitcoin is increasing the economic condition of the people, which will no doubt also put some good effect on the economic condition of a country.