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?