Please note, I am in no way trying to imply that our current highway system works well, but that is a far different discussion.
The high speed live won't carry freight, but it will free up space on the slower railway, and the motorway.
Additionally, the HSR proposal explicitly promised not to require ongoing subsidies. I think that was foolish: HSR would have passed without making silly promises.
Especially since we really do need to transition to a post-carbon future. Effective transit would allow us to increase housing density and commercial activity while decreasing per-capita use of fuel, water, and other resources. Leading to higher revenue from income tax, property tax, and sales tax, that does not show up on the train’s own profit/loss statement.
We just have to be realistic about it. A problem of the California HSR is that the officials have been coy with the actual numbers. Perhaps they are spooked by the disaster that has been Amtrak: Slow, expensive to ride, yet still losing money. We need to recognize that a good rail system can be subsidized, and still give a net benefit to the community and the government.