Not picking on this one particularly, but many of the posts in this thread seem to be based on the "broken window fallacy". Bottom line: instead of having a city and a hundred billion dollars, we will instead have a city and no hundred billion dollars. The nation will be poorer by that amount. The benefit to contractors in LA will be matched, and then some, by losses to other areas in the economy.
These things always stimulate economic growth. (as long as the petro thing doesn't hurt to badly)
The pie will be made bigger, not just cut up differently.
The dollars spent generate other dollars creating net economic growth.