The great fear of environmentalists is that China and India and other rapidly-developing countries will achieve something like the USA's resource consumption and CO2 production levels per person, multiplied by more than ten times the number of people. The great fear of US military planners is that they will militarize to compete for these resources, especially Middle East oil.
If China's cities build SkyTran instead of freeways, both worries will be greatly reduced -- by at least a factor of 5 (200 MPG SkyTran / 40 MPG cars.) However foreign competitors will then have another nightmare. Far more people in far denser cities, organizing their rapidly developing economy around unprecedented specialization and speed of production, will form an economic juggernaut of fearsome proportions. However I'd rather compete to produce than to destroy; to educate than to propagandize; to build a 21st century of unprecedented prosperity and human welfare instead of the 20th's long sad detour into militarism and statism.