And those experts were at least operating profitable legacy businesses, so had _some_ empirical proof of their claims (to wit: their products worked, even if not as well as the Valley's).
Now, lo and behold, we have a direct test of open source software vs. Krugmanesque proclamations. Krugman is simply not qualified to evaluate Bitcoin. You think he knows SHA-256 from a hole in the ground? He'll say it won't work just like legacy payment providers thought Paypal wouldn't work. And then he'll start advocating that it be prosecuted once it does threaten him, and then he will lose.
If someone can reliably predict macroeconomic trends and manage risk, what's their excuse for not being filthy rich? If they're not rich, I don't trust their tallent. If they are rich, I trust they won't give away their secret formula.