In ths instance, I was arguing against 'intelligent design', not for evolution. If you argue that genomes are similar because of 'code reuse', you then need to ask whether similarities between genomes have characteristics that reflect reused code.
One major premise of ID is that design can be detected by scientific principles. You're arguing against ID by saying the designer's purpose is ineffable.
The incompleteness of a theory does not necessarily equal forfeiture or even the unwarrantedness of its scientific status. For analagous example, even though I might lack exhaustive knowledge of the ultimate purpose of the designer and sculptor of Mount Rushmore, that subjective inscrutablity does not preclude the immediate defeasible inference that the work was the product of intelligence, as opposed to wind erosion.
Cordially,