> I happen to disagree with the theory.
That's great. You disagree with it... without any counterarguments. What's the sand smell like that your head is buried in? :)
> How much of the value of ... webvan
Webvan? Dude... Webvan?
http://en.wikipedia.org/wiki/Webvan
Webvan died because its expenses VASTLY outstripped its earnings at the time.
But oddly, you didn't mention Flooz at all, which would have been a better (though still failing) argument than all of the dotcom bust stocks you mentioned.
http://en.wikipedia.org/wiki/Flooz.com
Flooz was killed first by a lack of adoption, and second by an FBI case due to a Russian crime syndicate using them for money laundering. And of course, it was centralized, which means it could be shut down.
Bitcoin is growing in adoption, suffers from no central authority, cannot ever be shut down, may facilitate money laundering although the US government seems to only be prosecuting obviously nefarious cases such as the Liberty Reserve case and the Ponzi scheme guy and leaving bitcoin itself alone due to its potential economic value. Cash also facilitates money laundering, and I don't see that getting shut down anytime soon.
> if people realize Bitcoin is worthless, they'll stop trading with it
And if people realize the US Dollar is worthless, they'll stop trading in it too. If you're saying that the value of something is what people believe it is, then this argument holds for anything of any value, which is always subjective.