Bitcoin unlike any other currency existing is decentralized, furthermore it is not run by capitalist and elitists, which I think is a good reason not to make bitcoin subject for taxation because although it is run by private sectors it is not run by private elitists. furthermore, we are anonymous when we enter the bitcoin world so I think it is impossible to track and tax the users themselves.
I agree that it is impossible that bitcoin become taxable but as a user of bitcoin, even we are anonymous, we can pay tax in other way. We pay tax but not in way directly from bitcoin, during the transaction of bitcoin we pay for the fee to other agency that handles it. Like if we have cashout our money, the bank which process it will add a fee which contain additional tax from it.