You don't need a separate currency since you can just create a company that will sell gold for bitcoins.
Someone selling gold for bitcoins at a set price is not a promise but only a temporary promise to exchange gold for bitcoins at that price and that temporary promise can change at any time. If bitcoins were backed by gold there would be a permanent promise to always sell gold for bitcoins at a set price. A temporary promise that can change at any time is very different from a permanent promise. Someone selling bitcoins for gold is very different than someone backing bitcoins with gold.
100% agree. It bugs me when people think that having a market for exchanging gold for bitcoins is as good as backing, or can even be compared to backing. If that's the case just use your goddamn FRNs, I guess those are backed by gold because you can buy gold with them.
I changed my mind about bitcoins not being backed by anything. Bitcoins are backed by general ignorance about the underlying nature of money. And by the way so are USDs. It turns out this type of backing works just great... until it doesn't.