The one that clinched it for me was an article pointing out that the large airports in California are at capacity and expansion is either expensive, or impossible. You either need to spend couple of billion each to expand those air ports, or throw the money at high speed rail.

Also the big expense is not the high speed rail part of the system, is the commuter rail part through the bay area and LA. That;s the expensive bit. Not the straight high speed sections through the central valley.