I think this is the fallacy of arguing the middle usually deployed against science. There's a great example of Futurama, where the evolutionary naysayer demand

I think this is the fallacy of arguing the middle usually deployed against science. There's a great example of Futurama, where the evolutionary naysayer demands an intermediate form, and Farnsworth shows him one... then he demands another, and Farnsworth shows THAT form... and this cycle repeats hundreds of times until Farnsworth has no intermediate form and the naysayer declares victory.