One of the difficulties inherent in challenging ESA listings and other applications of this heavy-handed law is that, at least in the court of public opinion (and too often in courts of law), you're up against the perfectly reasonable American fondness for wildlife.
Environmental groups understand that a weak case for an ESA listing can be overcome by finding the right species–not "right" in terms of the species' population status, but "right" in terms of the amount of sentiment it receives from the American public.
It is unfortunate that the litigation strategy of environmental groups appears to be to find the right characters for their story, rather than advocate for a sensible approach to endangered species management under the ESA (which would in many instances contradict their story). This week's Newsweek contains an article on the polar bear listing and the ESA generally. The first paragraph of the article sheds light on this fuzzy-feeling phenomenon:
Ten years ago, when environmental lawyer Kassie Siegal went in search of an animal to save the world, the polar bear wasn't at all an obvious choice. Siegel and Brendan Cummings of the Center for Biological Diversity in Joshua Tree, Calif., were looking for a species whose habitat was disappearing due to climate change, which could serve as a symbol of the dangers of global warming. Her first candidate met the scientific criteria—it lived in ice caves in Alaska's Glacier Bay, which were melting away—but unfortunately it was a spider. You can't sell a lot of T shirts with pictures of an animal most people would happily step on.