You cannot prove something is harmless. Thats literally the opposite of science... you can not prove a negative.
He does have the courtesy to recognize that his thinking goes against the scientific method:
"While evidentiary approaches are often considered to reflect adherence to the scientific method in its purest form"
But then he just declares that his principle is superior to the scientific method:
"In the case of ruin, by the time evidence comes it will by definition be too late to avoid it."
He knows nothing about biology or argiculture:
"The ecological implications of releasing modified organisms into the wild are not tested empirically before release."
(In reality, crop plants don't survive in the wild even if you release them. No more than farm animals would.)
But then in section 12.8 he goes on to explain why he actually knows better than people who actually have domain expertise in the relevant sciences. It is a crafty tactic: He almost manages to convince you that you shouldn't listen to experts, and then he cites that there is a historical track record of experts having been wrong in their subject domains. And that you should listen to outsiders like him.
Why? There are always many unknowns with cross breeding.
> transgenics
Not all GMO is taking genes from other species. Some, like this article, simply turn off the expression of a specific gene.
> The latter relies on the "genius" of the human
How is that any different than selective breeding?
> something which is inherently fragile.
We've selectively bread many species into very unhealthy breeds. Just look at many do breeds with hip or breathing issues. Selective and cross breeding isn't without risks either.
> We need honest conversation about agricultural biotechnology, both about the facts regarding its health and environmental risks and benefits, and also about how this technology fits with or conflicts with our values about large scale monoculture farming and big companies having too much influence and about the harm that some modern technologies certainly do to the natural world. Sadly, the essay by Taleb et.al. poses as objective argument but is clearly advocacy trying to hide in a rationalist’s clothing. It doesn’t hide very well, and in its deceit only further polarizes discussion of an important risk issue we do have analyze carefully, objectively, and honestly.
I think the bigger issue I have with this kind of argument (beyond the lack of solid scientific basis) is that we do so many things that are known to actually be terrible or have terrible ramifications if done wrong (burning coal, mining coal, removing mountaintops to mine, drilling for gas, drilling for oil, transporting gas and oil thousands of miles, &c) and yet very few people blink an eye.
The day every person who is concerned about the effects of GMO plants also is as concerned and vocal about the amount of greenhouses gases, particulate matter, as well as the toxic and radioactive chemicals released by coal powered power plants, then we can start to talk. Those emissions are known to be extremely dangerous to us and the environment. Yet, no one seems to care because they're used to it -- it's not a change.