To be honest, everything can be taxed even your bitcoin earnings. For example you bought bitcoins in 2013 for $300 and sold it today at $8,000. That $7,700 is taxable as income, the classification and how much it should be taxed will depend on your local laws. So you better check if how much tax you should pay. However, if you are holding bitcoins as it and profited because of the increase, unless you cash that out and sell it then there is no profit to speak off. Right now that is the only way they can tax the use of bitcoins for regular users, but it may be different for bitcoin exchanges.
it is just funny why some people will want to be stingy to the government after making such a huge amount of money. As long as people will still keep utilizing the exchanges to convert to fiat, which means fiat, will still keep being relevant and there is no way on earth tax will be averted as long as the government considers them to be making profit.
Until maybe the use of bitcoin becomes totally P2P and I can make payments to anyone without having to go through exchanges, we just have to deal with it.