Correct me if I’m wrong, but my impression is that this is only true if one excludes the capital costs associated with the railroad (tracks, right of way, and I think also rolling stock). If you factor in the infrastructure construction costs (and reasonable lifetimes for replacing rolling stock), a high speed trail line will never be profitable without significantly higher fare prices than are presently charged.
But that goes to further support your point that high speed rail can only be accomplished with government input.
To be fair, I think that the same argument can be made for the costs of interstate highway systems and passenger air travel.