The French satirical magazine Charlie Hebdo is a known instigator, its pages dominated by provocative cartoons. Years ago, the Catholic Church was its primary target, but as the assimilation of Muslims in Europe became a dominant issue, the prophet Muhammad became the subject of scathing treatment.

Ten staff members of Charlie Hebdo, including four cartoonists, were slaughtered in the publication's Paris office Wednesday for daring to cause offense in the name of free expression. Two policemen died as well in the ghastly slaughter. During the assassinations, the gunmen reportedly shouted "Allahu akbar," Arabic for "God is great." And as they fled, they said, "We avenged the prophet."

But this isn't about piety, it is about lunacy.

This wasn't the first time the magazine was attacked. In 2011, the Charlie Hebdo office was firebombed after the magazine published a spoof edition "guest edited" by Muhammad.

The first attack left Charlie Hedbo's staff undaunted, just as this attack led cartoonists and other journalists around the world to publish messages of solidarity and further provocation to Islamic extremists.

In nations such as France and the United States, with the powerful tradition of a free press, the potential for slights is endless. That's especially true when the subject of satire is Islam, a religion with many adherents who see any depiction of Muhammad as an intolerable insult. Anti-immigrant sentiment, economic hardship and policies Muslims find antagonistic, such as France's 2011 ban on burqas (full body and face coverings some Muslim women wear to cover up in public), have fueled tensions. France, like much of Europe, has become fertile ground for terrorist recruiting and the radicalization of lone-wolf actors. The men suspected in the killings seem to fit that profile.

But responding to slights with bloodshed is barbaric and intolerable. Did some Charlie Hebdo cartoons veer into bad taste? Yes. Were they meant to undermine the belief that Muhammad's image is forbidden? Yes. That's still no justification for soulless butchery.

This is not just about cartoons. In denouncing the attack, Secretary of State John Kerry said Wednesday, "Today's murders are part of a larger confrontation, not between civilizations -- no -- but between civilization itself and those who are opposed to a civilized world."

There have been no specific threats to this country in the aftermath of the Paris attack, but this outrage against our ally is a worry in New York, with our huge international population and history of terrorist attacks. Yet again, vigilance must be constant.

The response from France, Europe, the United States and free nations everywhere must make clear that violent attempts to intimidate free speech will never succeed.