These people's theories (except Turing) are highly speculative predictions about the future. They could be right but they are not analogous to the predictions we get out of epidemiology where we have had a lot of examples to study. What they are doing is not science and it is way more reasonable to doubt them.

The Moravec stuff I'd say is more moderately speculative than highly. All he really said is compute power had tended to double every so long and if that keeps up we'll have human brain equivalent computer in cheap devices in the 2020s. That bit wasn't really a stretch and has largely proved true.

The more unspoken speculative bit is there will then be a large economic incentive for bright researchers and companies to put a lot of effort into sorting the software side. I don't consider LLMs to do the job of general intelligence but there are a lot of people trying to figure it out.

Given we have general intelligence and are the product of ~2GB of DNA, the design can't be that impossible complex, although likely a bit more than gradient descent.