The argument is not about whether or not evolution is correct or plausible, but whether or not the classical Darwinian dynamic is the primary cause of speciation. Evolution is not a biological concept, but a mathematical one. Evolution is a basic systems dynamic. Biological evolution is just a particular expression of the mathematics.
There is no doubt as to whether or not biological evolution exists, since it is a mathematical necessity and evident in any case. The question is whether or not that dynamic is the primary mechanism of speciation. The argument is not about its correctness, only its scope in this particular instance.
Evolution is mathematically impossible. This can be demonstrated any number of ways using probability analysis. However, the simplest explanation I have heard, years ago, still holds: it's like believing that a tornado can blow through a junkyard of airplane parts and assemble a 747.