It was a different world back then (both the design and implementation of the Concorde). France and Britain both put billions into the program in the hopes of being on the leading edge of the supersonic revolution. Clearly they were the leading edge, but there was no revolution.
It was the small, slow 737 and A320 that really changed aviation. I can fly between cities for less than $50 (on special) in 2011. Price won out over service and speed.
I don't think price was the problem, it was scale. It's cheap and easy to fly a 737 because there are a lot of them, and there are a lot of parts and a lot of expertise on how to fix them. Concorde, not so much; there were only a few, and so there was no secondary market of parts and labor and extra planes.
Another problem might have been that Concorde was not priced highly enough. Today's first class costs as much as Concorde did, and it's twice as slow... and people still buy it.
The real problem was noise. Everything was predicated on being able to do cross-continent mach 1+ flights. When the US then Europe closed off faster-than-sound flights over land, that was it.
After that, it couldn't make money. Then everything else started to become more significant and you could see the writing on the wall.
Having an unassailable conventional military isn't a waste of money because terrorists are the US's primary threat--terrorists are the US's primary threat because the US has an unassailable conventional military.
I'll take the Taliban over the Soviets or Axis as a primary threat, easily. The couple of generations before mine worried about the bomb, and the generation before that worried about the Japanese landing in San Francisco. All we have to worry about is having airplanes hijacked? That's success, not failure.
Well, to be fair, our enemy was the Soviet Union when these projects were started, and stealth technology would have been very helpful in a war against them.
It's interesting how the world has changed. Any political entity with the ability to make war has realized that wars do not help them get richer, and so everyone pretty much gets along. It's the people with nothing to lose that want to start wars now.
It was the small, slow 737 and A320 that really changed aviation. I can fly between cities for less than $50 (on special) in 2011. Price won out over service and speed.