For the sake of Bitcoin as a currency instead of commodity, we need it to be some kind of stable. Aren't we? Unless you only want to benefit from buying/selling like other financial assets.
It does need to be relatively stable, but not absolutely stable. Some people will desire to hold for the longer term regardless. For those people volatility is not so much a concern.
Also, as more goods and services become directly available for bitcoins swings in price relative to other currencies is less a concern. In the modern age of electronics and with the digital nature of bitcoins they can remain a usable exchange mechanism so long as their price remains fairly stable for a matter of minutes.