What are the limits of free speech?
The shockwave from the hail of bullets that murdered 12 French cartoonists and journalists at Charlie Hebdo in Paris in January continues to reverberate around the world.
They were not the first killings in the name of militant Islamism, nor the last.
That same day the next targets were Jewish shoppers at a Paris supermarket.
But it was the deaths of the French cartoonists and journalists that hit home in the western media, in a way that many thousands of other killings elsewhere in the name of violent Islamism have not.
The deaths at the magazine prompted waves of soul-searching about free speech, and whether cartoons that deliberately set out to offend are worth defending - especially when they sought to mock and satirize a religion and a figure that so many hold dear.
Even the Pope weighed in that month, as he flew from Sri Lanka to the Philippines.
On the plane travelling with him, we watched transfixed as he responded to a journalist's question about whether there were any limits to free speech.
Despite stating clearly and at some length that nobody should be murdered over what they thought or drew or wrote, Pope Francis had no doubt that there were limits.
Swinging his arm to demonstrate, he made clear that if his friend insulted what was most dear to him - his mother, for example - that friend could expect a punch.
It was not what many liberal fans of the Pontiff had expected.
And this week, the US has been finding out that it, too, has defenders of free speech who nonetheless believe that free speech has its limits, even before it veers into hate speech.
America may be a land built on the Bible and the gun - and a place that defends, vigorously, both freedom of religion for all, and freedom of speech.
But this has been a testing week for those who care passionately about that debate, creating strange bedfellows in defence of free speech - or rather, the right to offend.
It even united the initiator of the controversial "draw the Prophet Muhammad" cartoon contest in Texas, where two gunmen were shot dead after opening fire on a security guard, with the rather more left-wing supporters of PEN, an organization that campaigns for freedom of speech for authors, writers and cartoonists wherever they may live and work.
PEN decided to honour the dead at Charlie Hebdo for their courage in repeatedly satirizing Islam, despite an earlier firebombing and many threats to their lives.
Uncontroversial, you might think. But no.
Many signed a petition against the "Freedom of Expression Courage Award" being granted to the magazine.
They suggested it legitimized the content of the cartoons, which some saw as distasteful and unnecessarily, and repeatedly, provocative towards all Muslims.
Prominent writers who boycotted the PEN award:
Garry Trudeau, creator of the Doonesbury cartoon strip, surprised many when he spoke out against the award.
In his criticism, he claimed that: "Traditionally, satire has comforted the afflicted while afflicting the comfortable."
"Satire punches up, against authority of all kinds, the little guy against the powerful.
"By punching downward, by attacking a powerless, disenfranchised minority with crude, vulgar drawings closer to graffiti than cartoons, Charlie wandered into the realm of hate speech," he added.
Others then hit back against the objectors.
Then the shootings began in Texas - an outcome the cartoon competition's organizer was all too aware could result when she backed the project.
Before the 9/11 attacks, it is hard to imagine Texas having a "draw the Prophet Muhammad" contest.
And while few in the US will have much sympathy with the would-be killers, many ordinary people - religious or not - will be looking on in despair.
Because what is becoming clear is that the fundamentalism of this new generation of radical Islamists risks provoking an extreme reaction from some of those espousing the cause of unlimited freedom and liberty.
The danger is that tolerance and respect for our differences - and for each other - could be the loser; the very principles that many came to America and Europe to enjoy and uphold.