Why do MOST (not all) atheist automatically assume all christians are retarded?

I mean really Isaac newton, almost every president, Albert Einstein (at least for most his life) Justin Bieber, Glenn Beck, Martin Luther king Jr., Most people on the Spokane Shock, wright bros. Chuck Norris (He had like 7 different careers he has to be pretty successful) Elvis, Mr T almost all America's founding fathers, Nicolous copernicoun etc. where all Christians/ theists so where do people get off saying how stupid theists are?