People are willing to pay for supersonic flight. Concorde made a profit on most of it's flights, and it was only after the World Trade Center attacks and subsequent downturn in international commercial flight that it became a problem. Also, because not many Concordes were made, the R&D costs were never properly amortized.

The sonic boom however is an issue - Concorde was limited to a small selection of routes that passed mainly over water (e.g. London -> New York) because it was not allowed to go supersonic over a lot of countries. If you could fly supersonic all the way from London to Tokyo, or San Fransisco, or Sydney, then I'm sure it would be worth even more.