The unintended consequence of mitigating the many environment problems stemming from excessive burning of fossil fuels would be continued/increasing car dependency and the continued suburban sprawl for car dependency to exist within. Meanwhile, peak oil has coincided with peak debt, impairing our ability to rebuild railroad, mass transit, and water transportation systems that are far less oil dependent.
Kunstler sees American-style suburbia as the greatest misallocation of resources in the history of the world. What already exists will increasingly lose value and usefulness. Unfortunately, an enormous amount of capital will likely be squandered to prop these areas up. Much of the green renewable energy projects lack the ability to scale up (eg. solar, biodiesel, algae oil) and become serious energy resources. Skyscraper farms will require either artificial lighting for the plants, or the energy to rotate them around to expose them to sunlight; Kunstler sees this as an especially dumb idea. The fates of Phoenix and Las Vegas are sealed - they'll be strangled by a lack of water and the increased need for air conditioning. His other major point is that technomagic visions of a problem-free future are simply wishful thinking.
The 'bad news' about Kunstler's book is that its devoid of data - it's simply pages and pages of personal intuition. That doesn't create the necessary credibility to get his ideas accepted.