There two questions that we should be asking that are different than should we build High-Speed rail.
First, why is it so much damn more expensive in the United States and particularly California then everywhere else. And don't just jump to your single favorite answer like too much regulation or it's the unions or it's caltrans I suspect it's mostly the third one but that's another story.
Second, there's something wrong with the structure of our economy that we are trying to cause a massive interconnect between two regions that essentially do the same thing. There's no reason for so many people to go back and forth between Los Angeles and San Francisco. Both are fully developed modern cities that share 90% of the types of businesses that exist in one also in the other. There's no reason that most of the rest of that 10% couldn't equalize between these two cities. Are we building a permanent solution to fix a transient imbalance? Are we furthering the imbalance and creating a commuter system that only will increase the amount of people commuting and will saturate once again?
Mass transport really should focus on linking together regions that have to have differences in specialized production. Farmland, with cities, with heavy industrial zones, with regions where natural resources are mined, with forests, and with harbors that other resources from other regions of the world are transported. People should not be commuting from one city to the other they should either be able to find work in one megalopolis that's like the work they have in the other megalopolis, or they should move to the other megalopolis. There's just something fundamentally wrong with the structure of our society if you live in LA and you commute to San Francisco or vice versa.