Several reasons why this is bad:

How many fault lines will the train go over and what happens to a bullet train when there is an earthquake?

A 4 hour trip by train isn’t as good as a 1 hour trip by plane. Also you’ll have to go through security to get onto the train.

Is there enough traffic (people going to/from) from San Fran To San Diego to justify a $40 billion train that will likely be paid for with bond money and cost taxpayers a total of $80 billion (due to interest)? In a state with a $14-17 billion budget deficit this year?

A fixed bullet train rail line makes an indefensible terrorist target where air traffic lanes are effectively out of the reach of terrorists (too high).

If you want to save the planet, put more money into light rail because that is something that daily commuters will use and that is something that will actually get cars off the road.

anything that can be done to increase availability and convenience of public transport is a good thing and should not be criticized . It should be supported and more than commended.