Something you have to understand to understand the current balloon kerfuffle is that it highlights a psychological blind spot the U.S. military has suffered from since 1898.
Basically, the U.S. military doesn't think of the territory of the U.S. as a place where military events happen. It mentally divides the world into two spheres. There is the rest of the world (I think of it as "Over There"), which is where war happens. And then there is the territory of the U.S. ("Back Home"), which is a safe zone. Off limits. Back Home is a place where war simply does not happen.
American soldiers go to war Over There, and then they come Back Home to rest and recuperate. The idea that war might come to Back Home is so foreign to them as to be incomprehensible.
This blind spot has already bitten us hard twice, first at Pearl Harbor and then again on 9/11. When an enemy has the temerity to bring war Back Home, it knocks the American military mind completely off balance. Nothing is set up to defend against it, nobody is prepared to deal with it. Nobody is taking the kind of protective measures they would take as a matter of course if they were Over There. Because why would they? They're Back Home.
This mindset was already pretty hard to justify in 1941, and when long-range missiles got added into the equation in the '50s it became utterly obsolete. But it persists, because old habits die hard.
This is why something as simple as a balloon crossing into U.S. airspace can send the entire military-industrial complex into a frenzy. Because it doesn't matter that it's just a balloon. What matters is, these things aren't supposed to happen Back Home.