Almost beyond belief. In a piece on the Great Global Warming Hoax, Alicia Colon notes in passing that:

Even ex-Beatle Paul McCartney couldn’t resist swiping at Mr. Bush – a Harvard MBA still married to his first and only wife, a librarian – by saying: “After the last eight years, it’s great to have a president who knows what a library is.”

It seems like celebrity gives you a free pass to pontificate from a position of complete ignorance and/or stupidity.  The old saying “Ignorance is curable, stupidity is forever” applies. Most celebrities aren’t stupid, but many of them sure are ignorant.