Grizlason March 09 2011 09:30:39
""We often ask countries to do things that are good for the United States of America," said Allen Weiner, co-director of Stanford's international law program. "That may be hard for those countries to explain if it were on the front page," which justifies keeping the discussions confidential, he said."
This is the gist of it, I believe.
Although I'm not convinced, I can see how transparency might lead to populist politics and demagoguery.