I guess governments just found another opportunity to tax something, but in other hand it is indeed income so why shouldn't be taxed at all? In my opinion it should be free of taxes everywhere, otherwise it couldn't be truly decentralized. Its not easy question and as every hard problem should be discussed by many specialists from different disciplines together. According to wiki there are 7 countries that cryptocurrencies are banned in, and I found out there are at least 5 that are free of taxes