I am not defending Mayor Bloomberg, but the value of the newly created real estate on the lower east side WOULD offset a great deal of the costs. Remember, we are talking about some of the highest land values in the world. The reason things like this don't get done more often around the island typically involves blowback from environmentalists on the left, not the right. In this case, everybody wins. Whether sea levels are rising or not, the "hundred year storms" that happen just about every decade here have demonstrated how vulnerable the island (which sits a few feet above sea levels in most areas) and particularly its hundreds of miles of train, automobile, and other tunnels (which, of course are far below sea level) are to storm surges.
Again, I am sure there are things to hate about any plan Bloomberg comes up with, but this is a project that is about 100 years overdue for NYC.