At least when they're wrong, they usually don't lose millions of dollars. (But only... usually.)

I think some people are mentally modeling Ethereum as a sort of hobby thing in their head when they say things like that. I mean, who cares if my hobby static-rendering blog platform has a few bugs in it, right? But Ethereum aspires to be the foundation of an economy. Real foundations of economies have billions of dollars worth of effort poured into them. While a small set of particularly brilliant people may produce something that can run in this environment, Ethereum isn't what it would look like if they did.

I also think that people don't realize that the usual fate of a cryptocurrency is to die. Bitcoin isn't the first cryptocurrency by a long shot. Cryptocurrencies in general are not strong, robust things. I think something like Ethereum is quite likely, but there's no particular reason to believe we aren't three or four more major fully independent stabs at the problem away from a stable solution. Ethereum makes Bitcoin look like a homework problem in comparison; it would almost be beyond belief that we'd get it right the first time.