What if all those big corporates and businesses starts using crypto as a mode of payment just to avoid tax which will cause a direct loss to the government which uses tax for the betterment of the country. This might not affect corrupt countries as it doesn't matter because tax money goes to politician's coffers but what about developed nations?
Your thinking way too 1 sided. There is no way where you just avoid tax when you use cryptocurrencies to pay, or sell your goods or services for cryptocurrencies, it's still money and it will be taxed.
A cryptocurrency is still a form of money, it's similar to other investments that hold value, and if you got paid in gold, or bonds for example, those are still able to be taxed - it's impossible to avoid taxes in our world...
Crypto-currencies will be able to boost the income though, we will have a lot more freedom with money and it's an entirely new market sector where people are able to start new businesses and find new jobs - really expanding our markets.