LIKE kittens and libraries, marathons are intrinsically benevolent. They raise funds for charities, provide a day out for families, and present athletes with a demanding challenge.
Beyond the front-runners, the race isn't even especially competitive, since most amateurs are attempting to beat only their own personal bests.
Thus the double pressure-cooker bombing of the Boston marathon last Monday was perfectly designed to garner no sympathy whatsoever. It was contrived to be as appalling as possible in order to draw just the scale of outraged international coverage that the carnage has duly received. Of every stripe, terrorists eat denunciation for breakfast.
In the immediate aftermath, US commentators were universally defiant. Dennis Lehane declared in the 'New York Times': "You picked on the wrong city". The moment bystanders ran towards the first bomb to help their neighbours, "the primary purpose of the terrorists – to paralyse a populace with fear – was already thwarted. The little man or men who did this will, I have faith, be arrested, jailed and forgotten."
Calling for another Boston marathon to be scheduled as soon as possible, Thomas Friedman declared in the same paper, "We've been through 9/11. We probably over-reacted then, but never again. The right reaction is to "wash the sidewalk, wipe away the blood, and let whoever did it know that ... they have left no trace on our society or way of life".
Responses have been mercifully measured. Virtually no one has castigated the FBI or the police for having failed to anticipate the plot.
Most impressively, we've heard no gathering call for more draconian security at such occasions. Rather, 'Boston Globe' columnist Jeff Jacoby asserted that "we are not about to surrender our liberties and our heritage by going overboard in pursuit of safety".
Contrast this resolve to maintain business as usual with the airline industry's reaction each time a flight is targeted.
As every new attempt to blow up a plane is memorialised in yet another tightening of security protocol, the nightmare of flying anywhere now constitutes terrorism's greatest achievement.
Every time you remove your shoes in an airport is a victory for Richard Reid. Every time you throw out your water bottle before security, you pay tribute to the authors of the transatlantic airline plot of 2006. For future Boston marathons to be paralysed by X-rays of every picnic basket and all-body imaging of every six-year-old spectator would be a triumph for the culprits last week.
As Friedman noted, the biggest temptation in the face of mass malevolence is over-reaction. Therefore, in London, the police response to the mayhem in Boston has been perfectly calibrated and they did not call for yesterday's marathon to be cancelled.
So long as we congregate in crowds for any purpose, we run the risk that some ne'er-do-well will take advantage to inflict casualties. That is a risk worth taking. The alternative is turning the whole Western world into one big airport. With enough searches and metal detectors on every corner, pretty soon we'd all stay at home.
We don't yet know the flimsy ideological pretext these two young men of Chechnyan heritage, Tamerlan and Dzhokhar Tsarnaev, had for causing murder and mayhem.
But whether the killers are foreign or domestic, the constellation of underlying emotions is always the same.
Resentment, grievance, envy, mean-spiritedness, and contempt. Doubtless, delusions of superiority. It cannot be an accident that the Boston marathon is an occasion of festivity, of unity, of community – because to two disgruntled young men it represented a party to which they did not feel invited.
(How telling that the younger was flunking in university; that the older was also floundering, after having failed to make the US Olympic boxing team, his ambition to become an American citizen frustrated by an earlier domestic violence charge.)
That sense of having been left out traces back to fairy tales such as 'Sleeping Beauty', in which the evil fairy crashes the christening to curse the crib.
This urge to annihilate whatever seems to elude or exclude you is not the inclination of terrorists alone; it isn't only a problem for foreigners or disaffected outliers beyond our ken. It's all over the web.
Take a look at the shrill, venomous threads that run after articles just like this one. Take a look at the rancid blogs and vile tweets. Check out the hateful, spitting emails that sometimes land in my in-box. Recall the grotesque imaging of female genitalia over a photograph of Professor Mary Beard on the internet earlier this year.
Terrorism is merely a physical manifestation of the spleen that contaminates nearly all public conversation these days. The internet is awash in bile, sometimes so acid that it drives teenagers to suicide.
Vandals on the sidelines sneer at anyone foolish enough to make something or say something, under the misguided impression that demolition is a form of creativity.
Hence packing a pressure cooker full of nails, ball bearings and explosive and crafting an especially vicious, below-the belt comment on a website seem to entail their own admirable ingenuity, flair, and daring. Moreover, vitriol is every bit as commonplace on the left as on the right. If the internet is any guide, we are not dealing with occasional coteries of zealots with offbeat political grudges.
Apparently, a whole swathe of the human race feels ostracised, under-appreciated, sour, and fiercely resentful of anyone who seems to have found the happiness that life, or "society", or the rich, or the West, or immigrants, or white people, or the government, or the unjustly celebrated have denied them. Whether the weapon of choice is explosives or expletives, the underlying spirit of violence is identical.
All I can say is, God help us. We can search backpacks at marathons; we can track down culprits with meticulous examination of street-camera and mobile-phone footage and bring individual perpetrators to justice.
But the spite that drives acts of despoilment such as the one in Massachusetts is out there in buckets.
Blessedly, images of athletes and spectators forming tourniquets from their own sweatshirts, sprinting further to a hospital even after running 26.2 miles in order to donate blood, and carrying one another to safety sponsored the kind, brave side of human nature and gave me heart.
Likewise encouraging are the lone voices of reason, support, decency, and simple admiration in electronic forums – the people who refuse to be intimidated by the malice that too often characterises our communal discourse.
The "small, stunted individuals who would destroy instead of build" cited by US president Barack Obama in an interfaith "service of healing" last Thursday can be defeated, whether on the Boston Common or in the virtual public square.
Lionel Shriver is an American journalist and author