Typically I'm a free market guy, but certain things sort of need to be set up as common goods, and if they aren't then you're just getting crony capitalism where the state steals people's money at the barrel of a gun, builds a thing using the power of government to steamroll people who own the land, then hands it to their friends. Even if someone else had billions of dollars to build something similar they can't because they can't steamroll through all the stuff you would have needed.

Even if you use renewable energy (and let's pick a version like hydroelectric energy that we know can run for centuries once built), you have to consider the total environmental cost of building and maintaining massive rail lines.

In 2009 I did a study showing that if you used 30% of all renewable and nuclear energy on earth at that time you could replace the cement industry's use of fossil fuels with electric. The thing I didn't notice at the time is that the creation of cement inherently releases CO2 even if no fossil fuels are burned. In the year since, I've come to realize that limestone is in fact the only real geological term carbon sink, and stuff like trees don't hold carbon for very long in geological timeframes.

In the same study, I showed you could replace hydrocarbons as an energy source in producing steel if you used another 30% of all renewable and nuclear energy on earth at the time. The thing I didn't realize at the time is you can't create steel without coal because steel is iron and carbon, and the carbon comes from a derivative of coal.

In both cases, fossil fuels are also required to gather the raw materials. Mining is a fossil fuel intensive operation. Some people might counter with "but look at this mine that's fully electric!", but I'm aware of such mines and usually they aren't telling you about the fossil fuels they use. One mine I'm aware of claims to be "fully electric" but burns a city worth of propane every day in the winter to heat their mine air. It also conveniently leaves out the ancillary fossil fuel use since you don't deliver 30T rock trucks (or other supplies) hundreds of kilometers into the middle of nowhere with Tesla transports.

When you're talking about tens of thousands of kilometers of rail, the amount of steel and cement required are almost beyond human comprehension.

I forgot to mention that a high-speed rail system needs to have a much different level of workmanship compared to a regular rail. For example there are rail systems up in Northern manitoba, but those trains barely move, and so if you wanted to turn those into High-Speed rail you'd have to create a powerful foundation which would likely be made out of steel and concrete along with the rails themselves.