No currencies have a stable price and so is bitcoin. Anything that responds adequately to the forces of demand and supply can never have a stable price. You seem to be talking only about the fall in price. What of when the price of Bitcoin was enormously high? Don't forget that the currencies of some countries have almost no value.
bitcoin can well be just for investment and fiat money for typical day to day transactions. I would rather not use bitcoin to buy stuff online if I have some fiat money to use because the value of bitcoin is promising - I would just keep and hold of it along with investment here and there using my bitcoin.