Bitcoins do have cool features, but the features serve no purpose other than in the role of a medium of exchange.  Silver is useful for making mirrors and photographic film and wires and so on.  So the non-medium-of-exchange value of silver or any other commodity "backs" its use as currency.  Bitcoins have no non-medium-of-exchange value.

Because bitcoins have no usefulness other than as a medium of exchange, the value exchange ratio relative to goods and services is completely arbitrary.  For currencies that can be converted into commodities, the non-financial utility gives it some tether to stable price levels.

For fiat currencies with no tether at all, active manipulation is required to achieve stable price levels, but with bitcoins this is impossible by design.