Then it shouldn't subsidize airlines, trucking, and the automotive industry either. Nor should it subsidize the oil industry on which all of those forms of transportation are based. The current state of passenger rail is a textbook case of what happens when the government interferes with private industry and subsidizes competition.
The state should not subsidize business period. Corporate welfare is costs about $150 billion a year according the folks who have tallied up the tax breaks and subsidies that corporations receive.
High speed rail is a beautiful thing. I went from London to Paris is three hours flat on the Chunnel train. No hassle of getting to the airport, no crappy airline food, a great view of the countryside at 150 mph, no traffic jams to worry about.
Another consideration: we are running out of radio frequencies for communication with aircraft. When we do run out of frequencies, airlines won't be able to put additional planes to work, which creates a window of opportunity for high speed rail.