When a campaign stokes fear to promote its aims, it can't control the repercussions
Some important facts, such as motive and the killer's access to a gun, are not yet known about an idealistic British politician's murder - a woman who campaigned for her country to remain in the EU. Other key facts, such as her values, are in no doubt - that she believed in tolerance and inclusivity.
Yorkshire MP Jo Cox expressed this credo in her maiden speech last June, saying: "Our communities have been deeply enhanced by immigration, be it Irish Catholics across the constituency, or Muslims from India in Gujarat, or from Pakistan, principally from Kashmir." What struck her when meeting constituents from diverse ethnic backgrounds was that "we are far more united and have far more in common than that which divides us".
Jo Cox spoke up with conviction and moral passion for the kind of Britain she believed in. Our nearest neighbour is home to immigrants from numerous nationalities, especially the Irish.
Some 400,000 born in the Republic were registered there in the 2011 census, while as many as six million people in Britain have an Irish grandparent.
Here on the sidelines, it has been somewhat unsettling to watch the referendum transformed into a toxic debate on immigration, rather than a plebiscite on EU membership. It has been disconcerting too to hear Irish emigrants and their children complain about high levels of immigration into Britain.
The far Right has sown poisonous weeds during the Brexit campaign. But perhaps those roots are not deeply planted, judging by the public shock at Jo Cox's murder.
Hate-fuelled right-wing ideology does not represent Britain's values. Cox represented them. That reminder of British people's inherent decency is her legacy.
The Brexit referendum is an exercise in democracy, but something atavistic was unleashed during it. The insidious appeal of hate and prejudice reared its head. It has been transformed into a referendum on immigration, not EU membership.
The 'Leave' side has been run on the basis of whipping up fear and targeting the anti-immigration vote. In adopting these tactics, it has allied itself with the far Right - with the racial hatred peddled by those on the Right.
Prominent Brexiteers have indulged in Pontius Pilate hand-washing following the Labour MP's death, but they bear some responsibility for using xenophobia to attract support.
"Deeply saddened," said Nigel Farage in the wake of the killing. "Appalling," said Boris Johnson.
However, the politics of rage and prejudice promulgated by the Right were given credence in the mainstream, legitimised by Farage's acceptance into the 'Leave' camp by its leaders, Johnson and Michael Gove, Britain's justice minister. Farage even said he would be willing to serve in Cabinet with Johnson as prime minister.
Johnson said nothing to indicate that that would be a repugnant or unlikely appointment.
When a campaign promiscuously stokes up fear to promote its aims, it cannot expect to control the repercussions. Nor can it distance itself from them. Anger-mongering rhetoric can push an individual already on the margins over the edge.
The rhetoric of fear has been high on both sides of the debate, of course. "Cry 'Havoc!' and let slip the dogs of war," says Mark Antony in Shakespeare's play 'Julius Caesar' after Caesar is killed.
And that's what politicians have engaged in with their brinkmanship. But it has been a particularly noxious ploy in the 'Leave' camp because of the xenophobia.
Britain has been steered in an ugly direction. 'Take back control of our country' and 'Foreigners are taking over' goes the political discourse - one fostering antipathy and breeding division.
The implications are that Johnny Foreigner will put pressure on resources and British people will be left without - uncontrollable demand on jobs, hospital beds, affordable housing, the education system.
Jo Cox paid no heed to such polarisation: she campaigned for 3,000 Syrian children without parents to be allowed into Britain.
But she was stabbed and shot on the street outside her constituency clinic in an attack not just on diversity but on democracy.
Britain has a proud history of refusing to tolerate racial hatred. Enoch Powell was expelled by Ted Heath from the Conservative Party's shadow cabinet for his 1968 'Rivers of Blood' anti-immigration speech - and never held high office again.
He found a home with the Ulster Unionist Party. (I met him once at a drinks party. He wore his regimental tie and kept asking me to find him some "gobbles" - hors d'oeuvres, meanwhile insisting, with some irritation but without much conviction, that he had no regrets about the way his political career had fizzled out.)
Johnson's and Gove's readiness to accept Nigel Farage into their camp betrays a lack of political judgment.
In typically forthright fashion, Bob Geldof - on stage in conversation tomorrow night at the Dalkey Book Festival in Co Dublin - tackled Farage recently, calling him a "fraud". Johnson and Gove are arguably democratic frauds for trying to harness Farage to their own ends.
Thursday's killing acts as a wake-up call for public debate, which needs to be conducted more respectfully.
By all means, dissenting views should be aired, but they must be heard with courtesy.
Donald Trump calling his political rival Hillary Clinton 'Crooked Hillary' is a sign of that degeneration in public discourse standards.
In the social-media age, hate is all too easy to express under cover of a mask, used as a way of stifling opposition. The anonymity of Twitter ought to be challenged - people routinely use avatars and pseudonyms as cover for obnoxious ad hominem attacks on those with whom they disagree.
Does Twitter really have to tolerate the fake persona? Couldn't it oblige users to post under their true identities?
I don't seek to silence people but I do believe disguises should be removed.
Finally, while it was horrible to see Jo Cox murdered anywhere, there is something particularly loathsome that it happened outside a library - the repository for ideas. Such killings are anti-ideas.
Tributes and flowers are now flowing for her, but the real tribute to this passionate campaigner would be to endorse her sense of fair play and commitment to inclusivity.