Happy days are back for the sofa strategists and beltway bombardiers. After the miseries of Iraq and Afghanistan, a Libyan no-fly zone is just the tonic they need. If you zero in from carrier A, you can take out the Tripoli air defences while carrier B zaps the mercenary bases and carrier C zooms with special forces to secure the oilfields. You might tell the Americans to go easy on Leptis Magna after what they did to Babylon. Otherwise, let rip. You can sense the potency surging through Downing Street's veins. This is how wars begin, and beginning wars is politically sexy.

Last week saw a brief but fading moment of sanity from the White House and Pentagon. Both counselled caution against trigger-happy comments from Capitol Hill and Downing Street. US defence secretary Robert Gates pointed out that no-fly-zone is euphemism for war. It requires the elimination of air defences by bombing, and total cover thereafter. Since the explicit purpose is to help rebels bring regime change to Libya, the inducement to deploy ever more force if that fails will be irresistible. Hence the caution.

We now learn that a no-fly zone is back on the menu, with added adrenaline. All the familiar phrases are heard. Nothing is "off the table", and "all options are under consideration". Should the UN fail to offer a licence, there would be a "coalition of the willing". The only requisite justification for attack is a tear-stained girl pleading over the corpse of her brother on TV, or a car-load of civilians hit by a strafing fighter, or just a mob anywhere howling for help. Nobody likes being bombed.

So far the west's response has been tempered by possible counter-productivity. It is hard to imagine anything more calculated to please Osama bin Laden and jihadists around the world than the USS Enterprise, with British tugboat in support, steaming speedily towards the Middle East. For this reason cogent Libyan rebels have been pleading for the west to stay out of their conflict and not lend credence to Gaddafi's claim that the west wants Libya's oil.

No concept seems to carry less weight in military circles than that of counter-productivity. It is left to diplomats. If Nato knew the meaning of the word it would stop drone killings in Pashtun villages, shooting up buses, trucks and wedding parties and flattening Helmand villages. Counter-productivity appears to be a concept that gains currency only when a war is lost. The Americans in Vietnam knew massacring villages turned the rural population over to the enemy. They still did it.

While I have sympathy with William Hague in what must have seemed a low-risk covert operation that went wrong, it is odd that a specific rebel request not to put "boots on the ground" was so wilfully disregarded. We must assume that at SIS headquarters the James Bond urge simply overwhelms any consideration of counter-productivity.

Libya strategists are said to be torturing themselves over timing. Barack Obama says he "needs" Gaddafi to go, and David Cameron's position is much the same. Why this need is so pressing when, just months ago, Gaddafi was a dear ally and patron of western scholarship is a mystery. But in Cameron's statement on no-fly zones last week, Britain appeared to assert its right in international law to remove Gaddafi, as it did the Taliban and Saddam Hussein.

In this ambition he was supported by the leftwing international lawyer, Geoffrey Robertson, who claimed to have found a right for "states to render assistance to innocent civilians battling for their lives" wherever that might be. This right apparently "emerges or crystallises" not from any democratic decision but from "state practice, conventions, writings of jurists and dictates of collective conscience". To this is added the bizarre claim that a "responsibility to protect" the underdog in a civil war "devolves on to the security council" and, if not, on to any Tom, Dick or Harry. In other words, military aggression is anything you can pay a lawyer to justify. It is the Bush-Cheney theory of zero national sovereignty, and could be used to justify every aggressive war by Washington or Moscow over the last 50 years.

This legal cobbling-together of "rights" to justify military intervention is an invitation to global mayhem. But if Cameron has persuaded himself that Gaddafi must go because he is being beastly to his own people, what is he waiting for? Liberal interventionism nowadays is self-legitimising and self-authorising. Why hold back? Libya is a tinpot country of just over 6 million people, within easy reach of air bases in Cyprus, Crete and Italy. Britain occupied Suez in a matter of days in 1956. The longer Britain and America wait, the more likely is Gaddafi to build his defences and win other Arabs over to resisting "western imperialism".

The answer, of course, is that nobody wants to go that far as yet. Politicians want to "send a signal", offer vague support to rebels, and aid humanitarianism. There will be no mission creep. But what happens if the no-fly zone proves ineffective? It did not topple the Taliban or Saddam. That needed ground troops. Mission creep is the result of halfheartedness and imprecision in the initial stages of intervention. Eventually the aggressor is drawn into ground attack. Failure becomes "not an option", and a new nation must be built and expensively supported.

The craving of politicians to dust themselves in military glory is as old as the hills, embedded in leadership psychosis. However daft a war may be, however illegal, however unwinnable, politicians seem helpless before the sound of trumpets and drums. Considerations of prudence, economy or overstretch are nothing. That Britain has been fighting and not winning two wars already in Muslim countries seems to teach nothing in Libya. Jingoism never dies.

There is no point is repeating that Libya is not our country or our business. It was always going to be bloody one day. I find it incredible that Labour ministers, as they simpered in Gaddafi's presence, could have thought he would lie down like a lamb should his people rise against him. But unless we redefine words, he is not committing genocide and his brutality is hardly exceptional. If the rebels win it should be their victory, emerging from a new balance of power inside Libya. If they fail, they must fight another day. There is no good reason for us to intervene. However embattled they feel, Obama and Cameron should find other paths to glory.