Greenspan's policies consisted of easy money, dismantling regulation, and trusting big banks to regulate themselves.

Those policies failed miserably. Greenspan cleverly called the consequences of his policies 'irrational exuberance', and then failed to take action to rein in these consequences.

The crisis that resulted from Greenspan's incorrect analysis and bad judgement rivaled the Great Depression in its severity and longevity.

Greenspan's credibility is nil, so why should we listen to what he says about Bitcoin?

I might even agree with you that Greenspan's credibility as a shepherd of the entire US economy is nil. But the inadequacy of that conclusion to the actual argument at hand is obvious.

Short answer: because he knows much more about economics than we do.

I wouldn't be so sure. The Fed is the root cause of almost all the bubbles we've seen in US markets. As for Bitcoin he might be right, but I want to hear his opinions on economics about as much as I want to hear Obama's opinions on drone strikes.

Instead of appealing directly to the authority of Greenspan, you deferred to an appeal to the authority of 4 Presidents. Why should US Presidents be considered authorities on economic matters like this?

>Best part: your dismissal dings him for not calling earlier bubbles, in a story where he calls a bubble.

I think it's up to history to determine whether Bitcoin's a bubble or not. Rather than a bubble, it may simply be the first of a new type of digital commodity backed by computing power. There was a time when a domain like sex.com could be had for very little money. Now it's worth significantly more money. Is that due to being a bubble or simply it being prime real estate (which BTC might be compared to altcoins)?