Contrary to general opinion, Noir films do not just show the grimmer parts of American life.
Their particular effectiveness is to give you both the official version and then show you the unofficial reality.
It was a bit like public school and high school in my day : we got plenty of sunny uplift from our unaltered textbooks, '40s and '50s NFB films and present day CBC radio school broadcasts.
But just outside the classroom, TV's noir and sci fi horror movies , combined with tv newscasts, told us all was not really that rosy in the human animal kingdom.
Of course, learning in school and on television about good old Uncle Joe Stalin's Katyn Forest mass graves, Auschwitz, DDT, Thalidomide and Nuclear Fallout had already prepared us to trust film noir far more than any government official ....