President Francois Hollande's government insists freedom of expression must not be curtailed out of fear of further attacks, and authorities have got fully behind a spontaneous "Je suis Charlie" ("I am Charlie") social media campaign of solidarity.
But scepticism has emerged on the one hand from surviving Charlie Hebdo workers who reject some of the support for them as insincere; from others who found the weekly plain offensive; and others who question the human rights records of the 40-plus world leaders taking part in Sunday's unity march in Paris.
"There are so many big words being said about freedom of expression and democracy. But where was the support (for it) before? There wasn't that much proof," 26-year-old math student Nalo Magalhou said of some of the political and media reaction.
While far less popular than #JeSuisCharlie ("#IamCharlie"), the #IamNotCharlie hashtag has also appeared on Twitter.
Zakaria Moumni, a 34-year-old Franco-Moroccan draped in the French flag at the Place de la Republique rally point for Sunday's march has a very different reason to think there are cracks in the facade of unity.
"Some heads of state and government simply should not be there when they crack down on freedom of expression in their own country. It's hypocritical," said the former Thai box champion, who says he had been tortured in Morocco and had received support from NGOs such as Human Rights Watch when jailed there.
Morocco has rejected accusations of torture and last March filed a legal complaint in France against them.
For veteran Charlie Hebdo cartoonist Bernard Holtrop, the problem is with some of the paper's new "friends."
Holtrop, famous in France under the name of Willem, said he was happy if people worldwide marched to defend freedom of speech. But asked about support from Dutch far-right politician Geert Wilders, he said: "We vomit on all those people who are suddenly saying they are our friends."
"We've got a lot of new friends - the pope, Queen Elizabeth, Putin. I've got to laugh about that," he said. Willem says he is alive only because he does not like going to weekly staff meetings and was not in the Paris office when two gunman erupted and killed his colleagues and two policemen.