As a director, Bobcat Goldthwait has shown a talent for coming up with provocative high-concept hooks and backing them up with surprising human depth. Goldthwait’s disturbing satire God Bless America (Magnolia) isn’t as deep as it should be, but it certainly has a whale of a high concept, casting Joel Murray (best known as Freddy Rumsen on Mad Men) as an unemployed, divorced, middle-aged misanthrope who goes on a pop-culture killing spree, starting with the bratty subject of a My Super Sweet 16-style show. What follows is a violent comedy that turns on its hero as his mission curdles…