"Why does doomsaying dominate discussions about new technologies?"

From GMOs to plastics to energy it's a familiar pattern - I think the most important takeaway here is that the doomsaying is nothing new (Techliberation):

Clive Thompson notes that “dystopian predictions are easy to generate” and “doomsaying is emotionally self-protective: if you complain that today’s technology is wrecking the culture, you can tell yourself you’re a gimlet-eyed critic who isn’t hoodwinked by high-tech trends and silly, popular activities like social networking. You seem like someone who has a richer, deeper appreciation for the past and who stands above the triviality of today’s life.”

[...]Put simply, there exists a wide variety of explanations for why our collective first reaction to new technologies often is one of dystopian dread. In my work, I have identified several other factors, including: generational differences; hyper-nostalgia; media sensationalism; special interest pandering to stoke fears and sell products or services; elitist attitudes among intellectuals; and the so-called “third-person effect hypothesis,” which posits that when some people encounter perspectives or preferences at odds with their own, they are more likely to be concerned about the impact of those things on others throughout society and to call on government to “do something” to correct or counter those perspectives or preferences.

Some combination of these factors ends up driving the initial resistance we have see to new technologies that disrupted long-standing social norms, traditions, and institutions. In the extreme, it results in that gloom-and-doom, sky-is-falling disposition in which we are repeatedly told how humanity is about to be steam-rolled by some new invention or technological development.