Does Abu Qatada play World of Warcraft? Did he once, like Anders Behring Breivik, dedicate a sabbatical year to "hardcore" playing of the game? We don't know. Perhaps we will find out when Abu Qatada, often described as the spiritual leader of al-Qaida in Europe, finally faces trial. But I wouldn't bet on it.

For when alleged jihadists like Abu Qatada have been brought to trial, they don't quite get the treatment accorded to Breivik this week. If they are allowed to testify for five solid days, given an extended opportunity to expound their worldview, then the world's press do not hang on their every word, reporting in tweet-sized nuggets the nuances of their philosophy. Nor are their personal life histories, their psychology and video game habits, probed and debated.

Of course comparisons are tricky, not least because those who have staged the most lethal acts of jihadist violence – in New York, Madrid or London – have rarely lived to stand trial. But take this contrast. In Oslo, the court has been listening to a man who planted a bomb that killed eight and who went on to murder another 69 people, mostly teenagers, on the island of Utøya – a death spree Breivik described yesterday in terms that stop the heart. There has been copious discussion of Breivik's psyche and especially his views, starting with his courtroom lament that Norway had become "a dumping ground for the surplus births of the third world".

Contrast that with the airline bomb plot of 2006, in which an al-Qaida cell in Britain planned to blow seven transatlantic jets out of the sky. News reports of that trial offered a scant few lines about the conspirators' individual motives, with most of the coverage focused on operational details, the mechanics and scale, of the planned attack. My Guardian colleague Vikram Dodd, who covered that London trial, was struck when he heard a Radio 5 Live phone-in this week that was regularly interrupted by snippets from Breivik's statement. "The grammar of the coverage was as if this was the chancellor giving his budget," says Dodd.

More than one caller to that programme, while quick to insist they disagreed with Breivik's methods, did rather think the Norwegian had a point about multiculturalism run riot. "I can understand where this guy's coming from," said Tom from Dover. Several readers of a Guardian article sought to post comments in the same vein, calling for "a complete stop of immigration from Muslim countries" and suchlike. To listen to it, you'd think Breivik had simply wanted to start a debate, that he'd perhaps written a provocative pamphlet for Demos, rather than committed an act of murderous cruelty.

It was to avoid precisely this problem that the US Congress acted to relocate the prospective trial of Khalid Sheikh Mohammed, the alleged principal architect of the 9/11 attacks, from federal court in Manhattan to a military tribunal at Guantánamo. They did not want him enjoying the platform so gleefully exploited by Breivik. Perhaps they understood what the latter wrote in his 1,801-page manifesto, posted before the Utøya killings: "Your trial offers you a stage to the world."

The comparison is not so far-fetched. Breivik has expressed his admiration for al-Qaida's willingness to "embrace" death and was keen to adopt the organisation's methods: his ultimate goal last July was to behead Norway's former prime minister and post the video online. Like al-Qaida, he believes in acts of spectacular violence as a first step to changing the world, seeks to purge his own people of those deemed weak in the face of the enemy, yearns for a pure, past golden age that never existed, and dreams of apocalypse. Above all, he wants those he regards as his people to be unsullied by contact with inferior others. In this, Breivik and al-Qaida are kindred spirits.

What, then, is the right way to bring such people to justice, whether Breivik or Khalid Sheikh Mohammed? The cost of the Norwegian approach is that, by treating Breivik like any other defendant, the courts have given him that global megaphone. That represents a perverse reward for his actions: he would never have got such a hearing had he confined himself to ranting on a blog. More alarmingly, the Oslo trial has surely supplied an incentive to any would-be Breiviks: kill as he killed and you too will get the attention of the world.

And yet, by trying Mohammed behind closed doors, the US too has handed the forces of terror a kind of victory. They have declared there are limits to the open society, that the rule of law is not strong enough to cope with every eventuality. In a small way, they have conceded ground to the terrorists' view of the world. How much more appealing is the message of the Norwegian PM last summer, who declared his country would respond to Breivik with "more democracy, more openness and greater political participation".

Whichever approach we take to such crimes, Oslo's or Washington's, one duty is surely clear: we have to be consistent. We cannot apply different standards to terrorists depending on whether they are fanatics of the white supremacist or jihadist variety.

And yet we do just that. Scott Atran, an eminent anthropologist who has briefed American officials on the nature of terrorism, explains that we adopt radically different approaches depending on whether we believe the threat is from within or without.

Outside attackers, like the 9/11 hijackers, are treated only in terms of the impact and consequences of their actions; those who come from "our side", as the Norwegians see Breivik, are examined for their intentions, what made them act the way they did. Witness the case of Robert Bales, the US soldier who murdered 16 civilians in Afghanistan. "When it all comes out, it will be a combination of stress, alcohol and domestic issues – he just snapped," said the US military spokesman. It was personal, not political. Had it been an Afghan soldier killing Americans, it would have been the other way around.

It's clear why we might do this. We can unite against an outside enemy; if the threat is from within, we want to believe it amounts to no more than a single, lone madman. "People don't want to probe," says Atran. "They want to be reassured." But this division, instinctive as it might be, is not really defensible. Terrorist murder is terrorist murder, and we need to treat it that way – even when the killer looks like us.

Twitter: @j_freedland