This is an oft repeated fallacy by blockchain enthusiasts. Skeptical predictions from the past that turned out to be incorrect in hindsight has absolutely zero relevance to the viability of blockchain technology.
It's not "fair" as far as logical argumentation is concerned because the statement proves nothing since it is equally true of successful technologies as it is of failed technologies. It is an absolutely meaningless platitude.
Airing skepticism of a technology does little more than fuel forum fights after all.