Who is suggesting building high speed rail from Chicago to LA? Why would you pick that particular example? It takes even longer to drive, and yet we have built multiple highway routes that connect LA and Chicago.

Instead of picking dumb examples to discredit the idea, how about looking at obviously good places: The entire East coast from Boston to Miami would be a good corridor to build in. Or start in Chicago, Dallas, Atlanta, and build links to cities between 200 and 500 miles away, where taking a high-speed train would be faster than either driving or flying, and extend from there. Eventually you will have a network that can take you from Chicago to LA, even if that's not the sweet spot for the type of transport. And honestly, a 10 hour train ride will take only 3-4 hours longer than the equivalent flight, once you factor in the huge overhead of time involved in flying.