Bitcoin wasn't designed to replace gold; it was designed to replace fiat currencies. There is a marked distinction. In the long term, bitcoin should stand on its own, but in the short term -- during the transition period -- bitcoin will be attached to a known value, such as gold, whether you like it or not. It's the market at work. Today, it is attached to myriad fiat currencies. This works, for now. But it cannot last.
I think you are confusing backing and measuring(or what you call attached).
Bitcoin is measured in dollars as is gold and everything else out there.
People measure the value of things by using the money they are accustomed to. When you go overseas to say UK, you will in the back of your head convert the GBP prices to SGD because that is what you are used to measuring in. That does not mean GBP or the stuff you buy is BACKING your SGD. A backing is a promise to exchange at a fixed exchange rate.