You are right, but this implies that a “backed” currency does not have to be backed by actual commodities, just by the publics trust in it’s value. The problem is getting a cryptocurrency accepted enough so that you can use it to buy stuff. It’s kind of a vicious circle, nobody accepts the currency because it’s not a generally accepted method of payment, and it’s not a generally accepted method of payment because nobody accepts it. That’s the problem, that’s the obstacle that a cryptocurrency has to overcome to break the stranglehold of taxable government money. Now you see how creating the perfect currency from the beginning can’t work, it has to come in increments. First, we need an anarchist PayPal, a way to secretly wire the old government fiat currency without it being taxable, preferably on mobile devices. Once people are comfortable using that (and they will because it’s so efficient without taxes), these online credits will merge into new currencies that are more and more detached from government money. At first they are purely fiat, then currencies that are backed by commodities will emerge.
Edit: Or we need a rich libertarian institution that backs the cryptocyrrency by making it convertable into government money.