There are various reasons why supersonic transport is not widespread. Environmental impact is one. Lack of demand is the other. However, if the demand were there, it could be done these days. Concorde runs at an operating profit, remember - in other words, it covers its costs. And this is old technology - we could do at least twice as well as that, these days - in other words, halve the cost of supersonic travel. You'd need to add a lump to the fare to cover development costs - and it's the size of that lump spread over a small market that has prevented development up to now. The argument about kinetic energy is nonsense, however. Of course, you need to convert potential energy (fuel) into kinetic energy to accelerate the aircraft. But that's what engines are for. If you can get things into space (escape velocity 12 km/s [?]), then Mach 1.8 is hardly a huge mountain, relatively.
And yes, on a longish flight, in a nearly full aircraft, the specific fuel burn (kg fuel per pax per km) is not far removed from that of a car. Aircraft do go faster (more drag) - but they are in thinner air, and experience less resistance from air than cars do from roads. Also they travel in a straightish line, and cars generally don't. And their engines are **substantially** more efficient than car petrol engines.