"Never attribute to malice that which can be adequately explained by stupidity."
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
"Nothing in the world is more dangerous than sincere ignorance and consciencious stupidity."
-Martin Luther King, Jr.
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt."
I couldn't find Teddy's quote but thought these might help.