You may not be able to use Bitcoin to avoid taxes legally, but from a practical point of view as long as you can still conduct Bitcoin transactions anonymously you can use Bitcoin to avoid taxes.
Of course, if you can keep all your trading in a closed system, that would be very difficult to impossible to tax correctly. But that's nothing intrinsic to Bitcoins. In fact, whatever else you can trade in such as gold, cash, collectibles, seashells or whatever, is probably more suited for avoiding taxes since you don't have to worry about the public ledger.