In a review of various retrospectives on the Kennedy assassination, Tom Shales uses one of my least favorite think-piece tropes:
Was the terrorist attack on the World Trade Center and the Pentagon a greater shock than the assassination of President Kennedy? Perhaps not, on the grounds that you can lose your innocence only once -- have it ground with a black boot into dust only one first time. Everything that follows is, no matter how horrendous, by definition anticlimax.
It always bothers me when people project "loss of innocence" onto the nation or species as a whole. I can't read anything Mark Twain ever wrote and continue to believe that the US possessed any state of innocence prior to the 20th century. But if you believe newspaper and magazine writers, we end up living through so many losses of innocence that it's hard to believe anyone could ever have had so much innocence to begin with. Just in my own lifetime there was Vietnam; the myriad terrible things that went down in 1968 (when fate inflicted Matt McIrvin on a disbelieving world); Watergate; the Tehran hostage crisis; the Challenger explosion (but not the Columbia crash, somehow); South Central and OJ and Oklahoma City and the Columbine shootings and Sept. 11 and so on and so forth. We've lost our national innocence even more times than we've beaten the Vietnam syndrome. I'm pretty sure it was common to describe World War I as a loss of innocence; I don't know if the line was popular before then, but it's hard for me to imagine it not coming up over the American Civil War. Political movements frame themselves as a yearning for a return to pre-loss-of-innocence days, or accuse one another of being stuck in an innocent fantasy world.
Elsewhere in the piece, Shales admits that he's speaking for his baby-boomer age cohort, in which context it perhaps makes sense to speak of the killing of JFK as a moment of loss of innocence. My parents (who miss being boomers only by a technicality) certainly talk that way sometimes.
I think this is the key to the whole phenomenon: what you regard as a loss-of-innocence event is going to depend on how old you are and the age at which you became somewhat aware of big current events. The Columbine shootings didn't affect me that much, but they seem to have been tremendously significant to people who are just a few years younger than I am. The events following the beating of Rodney King filled me with apocalyptic racial guilt; the O.J. Simpson circus, the weird respect given the Unabomber, and the 2000 election had me questioning my very perception of reality. The World Trade Center and Pentagon attacks whacked everybody in the gut something terrible; the events of the subsequent couple of years have gotten me doing a lot of tortured and self-contradictory political thinking, of a sort that I think any serious adult eventually runs into in some context. Did any of these events constitute a loss of innocence on my part? I think it was gradually leaking out of my ears the whole time.
For that matter, my very first political opinion was that Richard Nixon was a good guy because he was the president, and it was mean for the people on the TV to pick on him. Later I learned the terrible truth. O loss of innocence! I also thought that Uncle Sam was the vice-president.
I think that when people talk about the country losing its innocence, what they are really missing is the innocence of their own childhoods, when grown-ups took care of the hard stuff (if they had childhoods easy enough that that was the case), and if some of it was nasty, the kids didn't really need to hear about it.
Oh, yeah, and: a lot of that perceived innocence of children is the result of fuzzy memory anyway. They may not be paying attention to national politics, but it's only because they've got their own vicious politics to work through.