Bitcoin is only one piece of the puzzle. If shops showed prices in whatever currency they find most liquid to keep the business running, to pay by bitcoin you'd need on-the-fly currency conversion without having to go to the exchange and buy bitcoins.

Speculators and Traders play a very important role in the bitcoin economy. They make sure there's always come bitcoinage available for purchase. Otherwise you'd have to knock on doors of miners to beg people to sell you some (if you knew where to knock).

If you want stability, I'm sure you'll be able to find people who could provide a good stream of bitcoins at prices well above current market rates that are almost constant. For example, if there was an imaginary exchange that only sold USD for BTC at a constant rate of 60USD/BTC (much higher than market value) would you be happier because of stability?

Lack of exchange rate stability only stops people from having fixed BTC prices, which is probably a good thing - hardly anyone has an intrinsic "feel" for how much things should cost in BTC, so a conversion/comparison will be necessary for quite a while.