It will not get you to SF from LA in 30 minutes. You have to get to Sylmar, which is a hike, then get through a security checkpoint; when you get to the other side, you have to drive from Hayward to San Francisco.
HSR plans get around this by terminating in the middle of major metro areas, which they can do because they get to reuse existing rail lines.
Trains don't need security checkpoints because trains follow a fixed route - you can't hijack them to cuba, you can't crash them into a building. All you can conceivably damage is the train line itself and the few people in it...and that sort of attack could be done almost as easily from OUTSIDE the train as from inside it.. Our impulse to PUT security checkpoints all over the place is idiotic. The TSA goons haven't won yet when it comes to subways and ski lifts and Amtrak and individual cars (as they enter tunnels or approach bridges) and we shouldn't assume they'll win on this one either.
HSR plans get around this by terminating in the middle of major metro areas, which they can do because they get to reuse existing rail lines.