Terrorists from a religious cult so reactionary you don't have to stretch the language too far to describe it as fascistic attack a school. The assault on a civilian target, filled with non-combatant children, has a grotesque logic behind it. They call themselves "Boko Haram", which translates as "western education is forbidden". The sect regards learning as oppression. They will stop all teaching that conflicts with a holy book from the 7th century and accounts of doubtful provenance on the life and sayings of their prophet written hundreds of years after he died.

A desire for sexual supremacy accompanies their loathing of knowledge. They take 220 schoolgirls as slaves and force them to convert to their version of Islam. They either rape them or sell them on for £10 or so to new masters. The girls are the victims of slavery, child abuse and forced marriage. Their captors are by extension slavers and rapists.

As you can see, English does not lack plain words to describe the foulness of the crimes in Nigeria, and no doubt they would be used in the highly improbable event of western soldiers seizing and selling women.

Yet read parts of the press and you enter a world of euphemism. They have not been enslaved but "abducted" or "kidnapped", as if they will be released unharmed when the parties have negotiated a mutually acceptable ransom. Writers are typing with one eye over their shoulder: watching their backs to make sure that no one can accuse them of "demonising the other".

Turn from today's papers to the theoretical pages of leftwing journals and you find that the grounds for understanding Boko Haram more and condemning it less were prepared last year.

Without fully endorsing Boko Haram, of course, socialists explained that it finds "resonance in the hearts of many poor and dispossessed" people, who are revolted by "the corruption and flamboyant lifestyle of the elites". Islamism is recast as a rational reaction to local corruption and the global oppression of "neoliberalism", one of those conveniently vague labels that can mean just about anything.

Once, rightwing newspapers or ultra-Catholic or orthodox Jewish writers would have been the least concerned about the subjugation of women and the most willing to find excuses for religious persecution. But with the reliability of a speaking clock, it is leftwing writers of the 21st century who seek to minimise violent reaction if – and only if – the reactionaries are anti-western. (They speak out against the lesser crimes of the US religious right, without a thought for their own double standards.)

"The mechanical denunciation of the west," wrote the French political theorist Pascal Bruckner in 2010, "forbids the western bloc, which is eternally guilty, to judge or combat other systems, other states, other religions. Our past crimes command us to keep our mouths closed." He might have been writing today, so persistent is the belief that the west is the root cause of the only oppression worth mentioning.

But the appearance that nothing has changed is deceptive. It was always absurd, and in its own way racist, to blame the problems of the world on "the west". Leftists came to resemble American neoconservatives. The US right, or an element of it, thought American military power could solve any ill. The left, or an element of it, talked as if the west was responsible for all ills. Both were self-obsessed. Both believed that the west remained the motor of history while the rest of humanity were bit players.

The most grievous offence was the failure of solidarity. You cannot ally with what liberal and leftwing forces there are in any country from Afghanistan to Zimbabwe if your are blaming their oppression on colonialism, neoliberalism or any other "ism" that is buzzing around in your head. You will end up excusing your comrades' enemies instead.

If occidentalism was absurd in the past, it's preposterous now. Boko Haram is not reacting to western intervention in Nigeria, for there is none. The only way you can pretend the west is to blame is by agreeing that knowledge is "western knowledge", rather than the property of the entire human race, and that the education of girls is "western cultural imperialism" – a road that leads you to nihilism as soon as you step down it.

Meanwhile, we are moving faster than anyone expected to a new age in which China will be the world's largest economy. For the first time since the 18th century, the dominant power will not allow internal opposition or the Chinese equivalent of the campaigns on behalf of the victims of its foreign policy that we saw in Britain, France and the US in the last 200 years. We have not begun to understand the turn for the worse the cause of global human rights is taking as empires shift.

On the few occasions western leftists feel they have to justify themselves, they say they must dedicate their energies to challenging what they can change. They cannot influence the Taliban or Boko Haram, but can lobby their own governments. Even if you take these explanations at face value – and I don't – they have a Tory feel to them. Until recently, it was conservatives, not leftists, who said that "charity begins at home" and quarrels in faraway countries were no concern of ours.

Peter Singer, a great radical philosopher, made the old distinction clear with a thought experiment. Imagine you are passing a shallow pond and see a child going under. You know that if you save the child you will ruin your clothes. Should you wade in? Of course you should, everyone replies: "It would be obscene to put your desire to save spending £50 on a new outfit before the life of a child."

Why then, asks Singer, do you not give money you can afford to spare to save the life a child in Africa?

The majority of conservatives say the deaths of children they know nothing of are not their business. Leftists, and again I accept I am generalising, revolt against such parochialism. Yet when it comes to violence against civilians and, most notably, the denial of women's rights, they change the conversation to anything except the deeds of the criminals in front them. The girl can drown or be enslaved and raped. They have more pressing concerns.

More on Boko Haram and the kidnapped schoolgirls

'I'm scared of everyone': fear and mistrust after mass abduction

200 girls are missing in Nigeria – so why doesn't anybody care?

Nigeria's grief over the abducted school girls is uniting our country