The rising pessimism and negativity since 2008/09 is a global phenomenon. I think it's wrong and very US-centric to attribute that to 9/11.
The 2008 financial crisis and the rise of social media has probably more to do with the rise of millennial pessimism and negativity.
During the Red Scare, loyalty review boards were instituted and civil servants insufficiently 'American' were sacked in the thousands.
The loyalty boards and Hollywood blacklisting were definitely a change is society, but it was so slow moving that I wouldn't compare it to a shift like 9/11.
The world wasn't really different before and after something like the hearings of the House Un-American Activities Committee, even though that is what would be a likely event you'd associate with the Red Scare.
When I think of 20th century cultural events that had an shift in society, I think more of the Cuban missile crisis, the Challenger disaster, the fall of the Berlin wall, etc... shorter events (not necessarily instantaneous, but well defined times) where you could define shifts in culture to before/after.
One caveat.
It's safety first, unless they decide to go to war to ensure continued access to cheap commodities (Iraq) or to play weird sociopath power games (Vietnam).
It's going to be kind of rich when they ask people from podunk towns in "flyover country" to go fight their next war, after years of ridiculing them and decimating their local economies.
People nowadays complain that gay pride parades have gotten too corporate, but especially by companies that are willing to exploit people in other ways. But this is simply the playbook Google pioneered, to take good will around certain social issues and use it as a decoy while you pick people’s pockets and put your boot on their face. I don’t think we can understate the extent to which good causes have been infiltrated by bad corporate actors and how much that had undermined our trust in our communities.
At least that's what I got from it as an "elder millennial" (born in the very early 1980s).
While the financial crisis might be more of a root of all problems in Millenial and generations that followed minds it’s not where it all started (I am a Millenial)
Also don’t forget 2008 was the year of the iPhone. The year we started inching towards being an always on society.
