I disagree with the author that this a "brand-new" stereotype. America has always been described as aggressive, militaristic and heavy handed in international affairs, in my anecdotal experience as a European.
In these days of turmoil, trying to figure out what is going on and what could cause this, it is appalling to me that no one since to blame the elephant in the room: social media, the social internet and making it the core of our society was in hindsight the stupidest thing humanity has ever made. Don't go blaming the Russian bots or Chinese posters. The whole thing is making us more stupid, more entrenched, more vulnerable to massive manipulation of public opinion. And we go cry whenever they take away our algorithms (see the popularity of BlueSky vs Mastodon for example). Call me dramatic, but social media and Web 2.0 indirectly will cause the end of civilisation much faster and more effectively than mass media of old ever dreamed of. And we are still all here happily engaging with it.
It is very possible that Americans in the 70s where as dumb as they are today, no way for me to confirm it, apart from the fact that a lot of nonsense that's happening today was not happening then, so that has to count for something.
If it helps, the idiocy is not a purely American phenomenon but widespread and now affecting the younger generations. As someone with a Gen-Z sibling, the illiteracy of that generation, grown on Youtube and Tiktok, is utterly mind-boggling. A large contingent of them voted for conservatives and fascists just "for the memes." Back in my day, young people tended to be idealistic and progressive. Fighting for something. Hoping to be better and more open-minded than their parents. I squarely blame this shift on the social like-and-subscribe upvote-driven Internet.
The problem started with the "engagement algorithms". Surprisingly, radical and controversial content is more engaging, so people who spend a lot of time on social media tend to be enraged all the time (at their perceived enemy).
This is just another way of saying you don't agree with their views. One man's propaganda is another man's truth. Goes both ways.
The new thing to me is the turn from "smiling psycho that will knife you in the back" into a form of unabashed revelry in dumb brute posturing