A link between Los Angeles and San Francisco would be beneficial for both cities. The use of the Hyperloop would reduce what used to have to be a plane or helicopter ride to make the trip with any speed. The Hyperloop would reduce that time, and the carbon footprint of those travelers. If these aren't enough reasons, creating the hyperloop will be a great leap forward in transportation sciences.
I think that the Hyperloop should be built. While it is viewed by a lot of people as being too impossible and dangerous, I think that such a system is possible. I also think that it would be a popular way for a lot of people to travel and commute.
High speed traveling systems only work in places where there is exceptional population density. Such systems have been successful in Europe and Asia because those regions have much greater population density than what is found in America. One place in America where there is sufficient population density is California. The Hyperloop would be an American achievement and it could possibly inspire people. If anyone can do this, it is Elon Musk.
The capability exists to create this very innovative transportation system. It would prevent accidents, save energy, make trips much faster and take people off the roads (we are our own worst enemy). The funding for the project will likely be made back within a short period of time through ticket sales. It is expensive but then so is every transportation initiative. It is time that we use innovation as intended, to improve our lives and provide growth opportunities. This project could completely transform transportation by making it safer and more efficient.
No it shouldn't be built. It is going to cause more problems than it is worth, not unless they are going to make it big enough to not cause a tie up in traffic. They should be able to get the lanes wide enough, more than enough lanes for each direction without having to add lanes in the usual 5-10 year span of time.