That is the problem when bitcoin is backed by fiat which it should not be the case as it's value will be determined by a debt ridden fiat currency.
In point of fact, am even looking to "back" Bitcoin with silver by accepting Bitcoin in trade for silver. 
I just have to convert enough Bitcoin to fiat in order to pay the taxes, (which are minimal as I don't keep much on the trade in order to increase quantity).This is what I believe should be done in the exchanges; that is to allow the person to trade either gold, silver or other precious metal (platinum or palladium).