I sometimes get asked - always by supers - "what is the significance of 9/11?" They think that just because there have been violent supervillain attacks in the United States, that a couple of towers coming down shouldn't be a big deal.
9/11 was a big deal for the same reason that the OKC bombing was a big deal: it was done by mundanes. Don't know why this matters? Let me break it down.
When a supervillain knocks down a building, it starts a very definite chain of events. The Feds get involved, because any violent crime involving powers is automatically flagged as an act of terror. That opens the floodgates of Federal money, Federal law enforcement resources, and Federal jurisdiction. Next, whoever perpetrated that shit gets his ass nailed to the wall if the local heroes, ACTION, the FBI, or whoever can do it. Next, the owners of the building that got aced call their insurance company's claim representative, hand over the ACTION paperwork, and get paid. Next, the insurance company files the paperwork to put a lien on any stolen property the supervillain had that could have been recovered. Finally, they call up some local outfit, like the MTF, and ask them to do repairs. Again, this usually comes out of ACTION's budget, and is paid for by the American taxpayer. Democrats love this because it gives them an excuse to raise taxes. Republicans love this because it lets them appear tough on crime. Independents hate it, because I dunno, nobody votes them into office so they'll bitch about anything.
What you should have noticed about this sequence is that it's very cut-and-dried, and it centers around one guy - the villain. The Man just has to mobilize some force, ride in like the Lone Ranger, and put boot to neck. Americans lap this shit up like sweet, sweet candy. You think it's a coincidence we're a nation of cowboys? America saves the day in a big, visible way, and that makes everyone happy. Furthermore, it's preventable! You just lock that villain up, and you lock up any other villains you come across, and voila, no more buildings go tumbling down.
The invisible enemy
Now we go back to 9/11. Who did it? It took weeks, months, or years to puzzle it all out. It was the sort of crime that could have been done by anybody with the right motivation. It's the sort of crime that could still be done, despite the security theater the government has put in place since then. It's the sort of crime that an awful lot of people want to do, because of America's absolutely racist, intolerant, violent policies toward other countries. The CIA overthrow the democratically elected government of a country, put a man in place to keep the oil running, and then pundits and hawks talk about bombing them because they don't like Americans for some reason. Imagine!
There's no villain here to lock up. There's no bright costume to point at and say "it was that guy". And deep down, the people in power, and the American citizen, know that they're out of their depth. All of America's mechanisms for dealing with super-crime are useless against an enemy without a face. It costs millions to incarcerate a single super-villain, but it will cost trillions to fully prosecute a war against who America thinks its enemies are - and that war will create still more.
In short, America is dealing with an invisible, intangible, infinitely large enemy that it created, and that grows stronger with every attack. Wouldn't you be afraid?
Veteran villains' reactions
Why were veteran villains like me horrified by 9/11? Why did you see pictures of Professor Pulsar on television, weeping tears through his mask? First is obviously the wholesale loss of life. Few villains are willing to kill so many civilians, and many - I hope most - of us prefer not to murder civilians at all. But secondly, we recognized immediately, like the American All-Stars did, what must have happened, and what it would mean.
The stress of dealing with this new reality tore the All-Stars apart and paved the way for the formation of hero teams like the Icons and Team Lambda. Villains have felt the backlash in different ways. The upgraded security apparatus that America put in place has focused more scrutiny on us, the way it's focused on everyone and everything else. That's one more reason we dress in colorful costumes and battle heroes in casual slug-fests. We know what "serious" looks like, and none of us are eager for the hammer to come down. Pageantry and sportsmanship is better than an angry Fed.