"America is killing itself and the Republican Party is looking the other way," Le Monde wrote in a scathing editorial.
Stars Bradley Cooper, Jude Law, Patti Smith, Ethan Hawke and Juliette Binoche signed the open letter.
Publications including Charlie Hebdo and BuzzFeed were barred from the party's rally.
The leftist candidate's meteoric rise makes it impossible to predict what will happen on Election Day.
A French newspaper's extensive probe has found the terrorists at the Bataclan toyed with some victims.