When Boston went into lockdown last week, you'd have been forgiven for thinking you were observing a war-zone preparing for attack rather than one of the most civilised cities in the world.

The sight of streets emptied of citizens but filled with soldiers carrying guns, behind whom rumbled convoys of armoured vehicles so plated they could roll over a detonating bomb and still emerge intact, was chilling to say the least. A week earlier, before the marathon massacre and the hunt for the surviving bomber took this final dramatic turn, Boston was renowned as one of the most intellectually rich, cultured and liberal places in America.

A bastion of WASP values, where the preppy, privileged and well-educated wear Brooks Brothers suits as if it were a uniform, it is home to some of the finest educational institutions in the country – indeed in any country. A degree from Harvard, the oldest of America's universities, is a passport to a seat at the top table of influence and prestige in every walk of life; likewise from MIT, the Massachusetts Institute of Technology, whose reputation closely rivals that of its Ivy League cousin.

The place where America made a stand against British colonial oppression in 1773, it is the residence of one of the country's fiercest and most implacable critics. Noam Chomsky's ceaseless goading of the US's political policies and cultural standards, from his office on the MIT campus, is proof, were it needed, that this small, elegant city has a deeply liberal soul. Were Chomsky to live in the Midwest or deep South, one doubts he would emerge not only unscathed but feted. Yet for Boston, the presence of the nation's scourge, a man once voted "the world's top intellectual", is a badge of honour.

Of course Boston is not perfect. Like any city it has pockets of deprivation and poverty, violence and crime. But the brothers Tsarnaev, who were behind the Boston Marathon bombing, were not from its underbelly. To all outward appearances their experience was as good as could be. Since their immigration from Chechnya 10 years ago, when the family's landlord apparently helped them get into good schools, the younger boy Dzhokhar went on to attend a first-rate school (where Matt Dillon and Ben Affleck studied), won a scholarship, attended the University of Massachusetts and hoped to become a doctor. His older brother Tamerlan was proving himself a talented athlete. A regular at a martial arts gym, he once expressed the desire to box for America.

Although there's still much to emerge as the search to understand their motivation continues, there seems little to suggest the Tsarnaevs were victims. Quite the opposite, you could argue, given that in settling in America, they escaped a country in terrifying turmoil, as it went through a bloody insurgency.

Tamerlan's comment that there were "no values anymore" in America, and that he did not have "a single American friend" are less suggestive of someone rationally offended by the capitalist, irreligious lifestyle around him, and more of a man whose view of the world has been warped either by some form of mental imbalance, or by an ideological conviction that acted like rose-tinted glasses, except these spectacles blackened everything they surveyed.

Whatever the root of Tamerlan's and his younger brother's disaffection, it is hard to believe they could have been radicalised by the experience of American society and culture they encountered in Boston. If the Tsarnaevs could dream up their deadly spree while embedded in the heart of a society which, compared with modern Chechnya, is little short of nirvana, they were wilfully and incurably blind to the best America has to offer.

One is obliged to suggest that in whatever town and whatever part of the US these men had lived, the result would have been the same; it might even have been worse. For reasons we may never know these brothers appear to have turned themselves into live grenades, beyond the reach of civilisation and compassion. But if it is one day proved that such a well-governed and tolerant community as Boston was the catalyst for such murderous mayhem, then God help America – and, indeed, us all.