Earlier quoted context omitted.
That will be a great argument when one of these new varieties is, say 5% of world cultivation of any particular crop. We are decades away from that circumstance. This isn't even a slippery slope argument; it's more of a "moderately smooth horizontal plane" argument. Given the challenges that humanity currently faces, these sorts of low-effort Chicken Little objections would endanger millions of human lives, if anyone…
Producing enough food is not a challenge humanity faces. We have more than enough food. Distribution is the problem. Monocultural has also been a problem many times in the past, so calling it a "chicken little" objection is disingenuous.
It has in most cases been far more reliable, resilient, nutritious, environmentally benign, and just to produce and consume food locally, rather than burning fuel to ship it around the world while it's still edible. We put up with lots of externalities from agriculture, because it's important that humans have food to eat. We can't dismiss completely benign ag tech out of hand, for essentially religious reasons. I make no particular claim for these particular crop varieties, but your objections are ridiculous.
You're simply wrong about this, and it's not "disingenuous" to say so.