There goes that misconception again. In the end, nothing is "backed" by anything.
Not gold, not food, not housing, not dollars: It all boils down to supply and demand.
If there wasn't a demand for gold based on a combination of aesthetics and deeply
ingrained cultural traditions, it wouldn't be worth squat. The only thing that "backs"
gold is people's desire for it.
If you take this to the long term conclusion, bitcoins are not currently in the position where they can offer much other than speculative demand. For it to be a trading tool, you're right that it needs to be stable - no one wants to accept 1BTC for a house, when tomorrow it could be worth half a house before they can offload it.
There are tons of businesses now willing to accept bitcoins, but it's superficial acceptance. How many of them trade only in bitcoins? If the only way to access a good is via bitcoins, then the value of bitcoins is in being the only way to access this or that. Same thing that makes the USD valuable.
I know the superficial will grow until it's possible to live only on bitcoins, but that takes a long ass time, and there are tons of challenges before it gets to that. For now, the pioneers are here, and speculation is concomitant with them.