First off, it's important to note that the argument in question was a discussion of one possible outcome of a test of the ability of science to detect design.
You're misrepresenting this argument by overstating its claims. Considering the context of the statement, it is not fallacious, though I suspect that you just don't like the logical implications. It's rather obvious that if a discipline is incapable of telling the difference between hypotheses X and Y, then any claim that "it was X and not Y" is by definition unreliable. In the case of biology, if we assume it's impossible to detect the presence of engineering even when we know it happened, then it follows directly that scientific declarations of "it was not designed" are untrustworthy.
And I have challenged you to demonstrate this for us. I have explained the form necessary. Why won't you do it?
Consider the case of the insulin-producing bacterium. Suppose the I hypothesize a designer is responsible. To test that hypothesis, I would predict that the signature of genetic engineering would show up as an "out of place" gene in otherwise "normal" bacterial DNA (I could do a DNA comparison to show this). I can detect that the bacteria produce human insulin, so I could compare the "out of place" gene sequence against the known human insulin sequence. If my hypothesis is correct, then I would expect to find an excellent match. Now, since we're aware of the techniques associated with recombinant DNA, the presence of the human insulin gene sequence in an otherwise unremarkable bacterial DNA supports the hypothesis that a designer was involved in this case.
QED. There's your test. And I suspect that you were already well aware of the details.
The presence of an anomalous gene in any organism would certainly stir up a lot of research. You must realize, however, that there are many ways in which genomes are modified under natural conditions. Bacterial conjugation and viral insertion are among them.
A pervasive set of anomalies across all living things would definitely call common descent into question. So-called code skipping is not a particularly difficult problem. It's a consequence of not knowing the exact history of every species.
No I am not. The language was yours. If your argument was overstated, look at your own post for the fault. I would suggest writing what you mean in future.
QED. There's your test. And I suspect that you were already well aware of the details.
Thanks for at least giving it a shot. Maybe we can come back to what "normal" means, whether your deductions were reasonable and other issues later. For now let's concentrate on the fundamental flaw.
What is the essential difference between design and non-design? It is that design is intended. I knock a glass off the shelf. Water and glass shards are all over the floor. Was that designed or not? It depends on whether or not I intended the result. Was I angry or simply careless?
So, where in your procedure do you test that the purported designer intended to produce this human insulin producing bacterium?