There are many things to be concerned about, ecologically and economically. But if excessive optimism leads people to believe that these problems are only being made up by "doom-sayers" and "chicken littles" (like, say, the few who predicted serious fallout from the real estate derivatives market), then nothing will be done about them. Causing pain and suffering which could otherwise have been avoided or reduced.
Fortunately, there are serious people doing serious work to address potential risks. Articles like this one are primarily aimed at simple-minded people who can't really understand the hard questions, and need a certain amount of fluffy encouragement to keep them getting up in the morning.