Yasmin Alibhai-Brown: Sometimes government plots are actually worth believing in

First, a preamble. I really don't believe voters were programed by aliens to be good little royalists and to vote for the Tories last week, or that "reptilian humanoids" are in command of the universe (former TV presenter David Icke's marvellously dotty credo), or that Jews run the world according to the counterfeit guidebook The Protocols of the Elders of Zion, or in the most outlandish theories about 9/11 and 7/7. So no need to call in the men in white coats carrying a restraining jacket.

However, I am a sceptic and more so than ever, this week. Even in mature democracies, leaders withhold the whole truth and nothing but the truth. Free-flowing information on the net is helping to break through secrets and lies, but too much traffic is wild and unverifiable and even when the sources are immaculate, most users get off on the thrill of detection and lose interest after that. Those who don't, end up with other fellow doubters, locked in a hellish circle of disbelief, round and round, for ever. Even Julian Assange will find his influence is temporary and limited. And if not, the determined establishment will make sure of it.

After the execution of the murderous ideologue Osama bin Laden and the dishonest follow-up antics of the American authorities, why should we give credence to any statements coming out of the White House, or indeed our own ministers? He lived in an opulent mansion; he lived in a scruffy house in a compound; the place was bursting with arms and soldiers enough to blow up Pakistan; not really, one person fired something from a guesthouse and the compound contained more children than combatants; he used his wife as a human shield and fired from behind her; no he didn't ... Which version do we trust? The angry pro-Bin Laden mobs on the web are spinning their own yarns and excuses. The truth has evaporated in the heat and now we will never know. What's more, most will not care. People are content to let matters rest and get furious when nudged and asked to be a little less incredulous.

We know what happens. Official information is processed and packaged. The expectation is that we will devour it quickly without stopping to wonder what and why. Like shop-bought mashed potato it will slip in fast through the gullet and keep us fat and content. Only for some, it sits heavy in the stomach, and so, filled with wind, we raise discomforting queries. That makes us "conspiracy theorists", two neutral words that together have come to mean "mad, bad and dangerous". In the old Soviet Union, dissidents were declared insane, their concerns silenced – and Westerners rightly condemned the state. We are also right to condemn al-Qa'ida's use of dark methods to brainwash young Muslims in to taking up arms against the West. So why this coyness about Western opaque operations?

If Bin Laden had been tried by a sober, international panel of jurists we might have found out about US complicity in the making of him and the role of Saudi Arabia, Afghanistan and Pakistan, which have been playing games on both sides. The rules of war say that, when possible, enemy bodies should be returned to families for burial. A grave would have enthused a new generation of Islamicists but an unseen body thrown into the sea will inflame vastly more. Bin Laden seemed to be a spent man. So why this cowboy shooting? And why now? After "Birth-certificate-gate", was Obama trying to prove he really is American, in the style of Sarah Palin?

We have a democratic duty to ask difficult questions. The royal wedding made me think of Diana and her death – and how I still feel we have been lied to. Then I read that a film on the inquests into her demise cannot be shown in Britain but will be screened at this month's Cannes Film Festival. Unlawful Killing by Keith Allen bravely investigates the media and appointed inquisitors and their explanations of why the Princess said she was terrified she would be killed in an arranged car crash. "Just coincidence," say the great and good. If this was a "civilian" case, the police would not think it was a "coincidence" that a victim's expressed fears came true. Allen says he is exposing "a provable conspiracy theory after the crash". For his troubles, his reputation will almost certainly be incinerated in the rubbish heap of history.

For in this modern world, such probes are not allowed – and the very idea of public distrust has successfully been discredited. To be convinced of any manipulation or plot by the powerful in the US or the UK is to lose all standing and credibility. But if it is crazy to fall for conspiracy theories, is it any less so to unquestioningly accept establishment bulletins? Decades too late, some accounts are released which show how efficiently these governments can cover things up.

During the Cold War, US scientists tested "truth serums" on unsuspecting individuals to see if chemicals could get people to unload secrets. In Alabama, as part of a study, African-American men were injected with syphilis from 1932 to 1972 – and the crime was discovered only in 1979. This spring, after half a century, Foreign Office boxes were opened up to reveal that the British in Kenya sanctioned the torture of Mau Mau members and innocent people using tricks including putting snakes up the rectum and broken bottles into vaginas. When the historian Caroline Elkins first exposed these horrors in 2005, she was vilified by insider historians.

Our grandchildren will one day find out what crimes the US and UK committed against the Iraqi people of Falujah, and exactly how they and Arab dictators co-operated on "rendition". And what made inmates weep and lose their minds at Guantanamo. It is true that non-Western governments are much, much worse. But they don't hold themselves up as exemplary democracies.

In 1988, Katharine Graham, publisher of The Washington Post and member, with other major media owners and editors, of the immensely powerful Council for Foreign Relations, said in a speech to the CIA: "We live in a dirty and dangerous world. There are some things the general public does not need to know and shouldn't. A democracy flourishes when the government can take legitimate steps to keep its secrets and when the press can decide whether to print what it knows." Graham may have died but that ideology lives on because we, the people, allow it to.

y.alibhai-brown@independent.co.uk