New York Times article suggests that Huntsman's belief in the global warming hoax makes him "entirely too reasonable and mainstream for the contemporary GOP"

Cap and Trade Becomes a Bludgeon in Republican Primary Brawl - NYTimes.com

The sin of being "too reasonable"
...
Thomas Mann, a congressional scholar with the Brookings Institute, is skeptical about the effectiveness of Huntsman's position on climate change during the Republican primary.

"It makes him appear entirely too reasonable and mainstream for the contemporary GOP," Thomas Mann, a congressional scholar with the Brookings Institution, said of Huntsman position on climate change.