Why does herbert hoover get so much grief for his inability to prevent (or, indeed, his tendency to make worse) the onset of the great depression; and are those criticisms fair?

He gets so much grief because he became president after the Coolidge, Harding, and Wilson.  These guys started the mess by mostly supporting businesses and not the American people,(except for the rich).  He really didn't do anything wrong he just got stuck with their mess that they let behind.  It boiled over when he became president and their was pretty much nothing he could do to fix it.