I'd argue that crypto currencies are a fundamentally new asset class, neither fish nor fowl. To become a useful "currency," yes, stability is a desirable quantity. What it is "supposed" to do is not a useful concept here. What it does is much more important. Currently, bitcoin is still more a highly-speculative, bubble-prone asset class with some of the qualities of a currency, some of the qualities of a stock, and some of the qualities of an asset like gold. It is incorrect to pigeon-hole it as any one of these.