@mozella
I guess my point would be that the same problems of supersonic flight existed in 1963-1976 as did in 2003. It was a technological challenge, and it was expensive.
The physics of the sound barrier did not change over that time. Nor did the constituent gases in Concorde's exhaust plume*, nor did the volume of the sonic booms.
However, in 1976, going supersonic was considered worth the costs, and in 2003 it was not, and that was a political (or if you prefer, cultural) calculation.
*Actually, I think the engines were tweaked to be less "smoky", but that may have been before commercial ops began.