Why is "replacement" always the question? Why does it need to replace anything to be considered useful?

Bitcoin is an innovation and innovations always add to our lives. They don't need to subtract anything by replacing it. Besides, bitcoin and gold are not in the same category. While gold is a metal (physical object) used for jewelries, investment, etc. bitcoin is completely digital and is used as a payment system.

In fact the way I see it, with bitcoin we now have a real option for diversification that has no correlations with any other asset or market. An option that didn't exactly exist before.