The second your backed by something, there is an authority. Gold? Who own/store the gold, what if the gold get stolen or seize?
Backed by stocks? Who own the stocks, on what market? What about stock owning regulation?
No! The idea is to having something you can trade without the paperwork, anywhere to anywhere for anything, from a phone instantly & borderless.
If you like a backed currency, try your own and let the Bitcoin experient goes... time will tell!