The recursive (more correctly: inductive) argument is that there is no effect. It's like saying that no matter how many times you subtract 0 from a positive int

The recursive (more correctly: inductive) argument is that there is no effect. It's like saying that no matter how many times you subtract 0 from a positive integer, the result will still be a positive integer - because subtracting 0 has no effect on the functioning of the system (the two are "the same" - not just similar but exactly the same). Subtracting epsilon (an arbitrarily small number) is similar but the recursive argument breaks - if you do it enough times it's no longer a positive integer. The fact that your brain is already wired somewhat differently than since starting to read this comment doesn't have much to do with this argument. To break the inductive argument and prove that mechanical birds are impossible, what you would have to show is that there is some bone or ligament or muscle or feather or something else, where if you replaced it with a plastic/mechanical/etc version with the exact same properties and behavior, the flying system w=could no longer function "the same". In other words, that there is some bone or muscle or other mechanical thing that even in hundred thousand years, science could not replace with a non-biological version without making some change to the behavior of the whole system - that it could never be made "the same" even in theory. (I say "in theory" because it is quite likely that we could never do so with a neuron - the whole switching back and forth example is very far-fetched.) So it is only a thought experiment/inductive argument: not a practical statement about biology. One thing that is interesting to point out is that no birds have the carrying capacity of modern planes, but we haven't reproduced mechanical birds that function the same way birds do. Science doesn't really have a strong incentive to try to exactly copy the mechanics of a pigeon with plastic components and plastic feathers and ligaments and some kind of muscles, and trying to get it to be composed exactly the same way. Other than a novelty, it doesn't really "get us" anything. In perhaps the same way, science may not have any strong incentive to exactly copy humans into a virtual reality, setting up neural networks that are wired the exact same way, and feeding the virtual neural nets outputs exactly like a child would hear and see around them, etc. Even though very large server farms like Amazon's today have more memory and do more calculation than the human brains' neural connections imply (given our estimate of what actually does the computation), so that they're like "jets" and the human brain is like a "bird" -- still, there is no clear incentive to copy humans in a way that leaves the simulation conscious. What does a conscious simulation get us? What does a mechanical pigeon get us? So for this reason there is at least some reason to think that we are not about to build a conscious machine - we don't need it.