Here is my answer.
Bitcoin is backed by the full faith of those who do not trust governments.
in other words,
it's backed by nothing. just like gold. that's a feature, not a bug.
money being "backed" by anything requires centralization. this is why the idea of a gold-backed cryptocurrency (often floated by gold bugs like peter schiff) is useless. both gold and bitcoin derive their value from their network effect. people value them because
other people value them and use them for money. anyone who tells you that gold derives value from industrial use is ignoring the actual market share of industrial gold use. the only thing that matters in both cases is
network value.
here's a brilliant post from satoshi that explains this phenomenon. (he also explains why bitcoin is more attractive than gold as a value transfer network)
bolded for emphasis:
As a thought experiment, imagine there was a base metal as scarce as gold but with the following properties:
- boring grey in colour
- not a good conductor of electricity
- not particularly strong, but not ductile or easily malleable either
- not useful for any practical or ornamental purpose
and one special, magical property:
- can be transported over a communications channel
If it somehow acquired any value at all for whatever reason, then anyone wanting to transfer wealth over a long distance could buy some, transmit it, and have the recipient sell it.
Maybe it could get an initial value circularly as you've suggested, by people foreseeing its potential usefulness for exchange. (I would definitely want some) Maybe collectors, any random reason could spark it.
I think the traditional qualifications for money were written with the assumption that there are so many competing objects in the world that are scarce, an object with the automatic bootstrap of intrinsic value will surely win out over those without intrinsic value. But if there were nothing in the world with intrinsic value that could be used as money, only scarce but no intrinsic value, I think people would still take up something.
(I'm using the word scarce here to only mean limited potential supply)