I would agree with you that the quoted statement is not terribly persuasive. I was simply encapsulating the actual argument at hand, instead of the straw-man argument of "method versus outcome." And while the vagueness diminishes the magnitude of the evidence, I don't believe it makes it non-zero.
To your second point:
in the context of "it's been fine for 20 years but we're not sure about the really long term", I don't see how the "rapid and intricate" quality is relevant.
I would add to ChristianKI's apt reply that while conventional modifications via breeding can eventually have monumental effects, direct genetic modification can rapidly--over the course of a single generation--have monumental effects that may have unintended side effects attached to them due to a lack of understanding of the intricacies of genetic interactions.
I can't find any sense in ChristianKl's answer, but maybe that's just me.
My basic problem with your position is that "conventional modifications via breeding" are better described as picking from a set of random mutations those where the phenotype looks appealing. I don't know why you think it's a safe method, especially compared with making targeted genetic changes directly.
Basically: How does one pursue the truth when direct engagement with evidence is infeasible?
I came to this question while discussing GMO labeling. In this case I am obviously not in a position to experiment for myself, but furthermore: I do not have the time to build up the bank of background understanding to engage vigorously with the study results themselves. I can look at them with a decent secondary education's understanding of experimental method, genetics, and biology, but that is the extent of it.
In this situation I usually find myself reduced to weighing the proclamations of authorities: