Like everything, its all about tradeoffs: upfront costs, ongoing costs vs profit, time, environmental impact, convenience and capacity. All the transportation systems we should invest in (and all of them are somewhat subsidized by the government) should be the ideal balance of these tradeoffs for that particular distance range.

I believe there is a sweet spot in travel distance where high speed trains are the optimal solution over cars in the smaller distance range and planes in the longer distance range. Few would think to travel from LA to NY on a train but when you are talking about LA to SF, it makes a lot of sense. Time and destination wise it's more convenient, the environmental impact is less, frees up plane capacity at LAX and SFO for long distance flights, ongoing costs are similar, and the only question remaining is do these benefits outweigh the very large upfront cost? Would love to see how much these costs compare (a new high speed train route vs a hypothetical new airport + enough planes to service the route)