The fundamental problem with that reasoning is that in a vacuum, where the USA are not a military hegemony, the only nation that might be in position to have any interest in taking you on are Canada and Mexico. The VERY THREATENING Canada and Mexico, one might add. Maybe Russia if they're really desperate for bits of Alaska.
America doesn't need such a first class military for local defense. It needs it to be in position to impose its interests worldwide (preferably without fighting). And that's a lot more questionable.
We're not just defending the United States' literal soil, though. We're defending our interests abroad, manifest in the form of world peace between the great states and security for our allies.
The Pacific Ocean and the Atlantic Ocean might also have something to do with this...
I don't understand what this has to do with what I said?
But how much cost is neccessary for that security?
Would any country threaten the US without F-35s and F-22s?
Well, yes. Countries in the past
have threatened us when they didn't think we would or could do anything about it. It's sort of the story of the first half of the 20th century.
But even if I were going to wax prolifically about the glories of military spending in order to secure our borders against Pearl Harbor II, I'd be missing my own point. US acquiring and developing advanced military technology is the vanguard of future security. Yes, the world seems quaint and peaceful
now, but when we stop investing in next-gen tech, the next thing you know is that 20 years from now the Chinese have eclipsed us in every way that matters and start projecting into Southeast Asian, the Indian Ocean, and beyond. It's not just them, either: other admittedly less-competent states with designs and ambitions of their own would feel more at liberty to pursue their own aggressive diplomacy with whatever neighbors they think they have a right to. It doesn't have to be an outright war of conquest, but aggression has never been limited to "alright, all of this is mine now" throughout history. The United States, ironically enough, being a prime example of that.
The US army overextends itself too far and too often, and it is costly and
some might argue counterproductive. But the one department that is actually capable of being a guarantor of future security - not just for us, but our allies and the world at large - is the one that realizes that staying a step ahead of the game secures victory before the war is fought. And there is no way to do that when you pull the rug out from under your military.
And that is exactly the wrong approach. This leads you to spend far too much far too poorly, and in the end does not buy the security you were expecting.
It already has.