We are told that to fail in Afghanistan would endanger our security in Britain by making us appear weak in the face of Islamic extremism. If the Taliban were to regain control of Afghanistan, Al Qaeda would have a base from which to operate globally.
At least, that's the geostrategic propagandists view. The problem is I think it's far more complex. What the response to the events of September 11th did was not to destroy Al Qaeda but to fragment and disperse it with cells setting up in other countries while the original bases in Afghanistan were bombed to destruction. Indeed, Al Qaeda is now so disparate that it functions whether Osama Bin Laden is alive or dead.
The Taliban haven't gone away - indeed, from their new bases in Pakistan, they have returned and, especially in the south of Afghanistan, have become a serious insurgency.
Britain, as the lead member of the NATO force deployed to Afghanistan, has deployed over 9,000 troops mainly in Helmand. In the last 10 days, 15 of these soldiers have been killed and an issue which had been swept off the front pages by other matters has swept back to the top of the political agenda.
As the military position has worsened, so the political concensus is breaking down too. Both Nick Clegg last week (to the derision of the partisan Tories) and beleatedly David Cameron have started to ask some searching questions but the key question is simple: what is our objective in Afghanistan ?
I suspect the primary objective is to prevent the Taliban regaining power and allowing Al-Qaeda to operate freely. The Taliban might have been driven from Kabul in 2001 but they withdrew into Pakistan and therein lies the dilemma. It is believed that as in the Domino Theory in Vietnam, should Afghanistan fall into radical Islamism, Pakistan will fall too and the thought of an Islamist regime with nuclear weapons isn't one that goes down well in many world capitals.
So, we prop up Pakistan by propping up Afghanistan and maintain a military presence near both Iran and Russia too. In other words, by being in Kabul, we are at the centre of one of the most unstable areas of the world. To pull out would be to abandon southwestern Asia and possibly beyond to Islamism.
So we stay and we bleed because it's perceived there is no other option. The Americans might claim that the "surge" of General Petraeus in 2004 achieved a lot in Iraq but would a similar effort work in the vastly different terrain of Afghanistan which withstood a full-scale Soviet invasion in 1979 ? It seems unlikely.
The options are therefore to stay and bleed or to withdraw and face exclusion from a significant part of the world and a charge of weakness that would only strengthen our adversaries. It's a damning failure of policy that began long before September 11th but since 2001 Al-Qaeda and like-minded elements have spread worldwide and utilise means of global communication that no army can subdue.
I'm increasingly of the conclusion that it's time to cut our losses. Britain has shouldered a disproportionate part of the NATO burden and with our public finances in ruins, it's a burden we can no longer sustain. The Netherlands have pulled out and Canada is committed to an exit strategy too. In contrast to our efforts, the French and Germans seem much less engaged. IF our fellow NATO members can't or won't support the mission, it's time for Britain to review its position and, as in Iraq, begin to scale down our presence and consider withdrawal as a matter of priority.
There WILL be consequences if we withdraw from Afghanistan and they may stretch all the way to the streets of London but as July 2005 showed, terror can sometimes be homegrown too. It takes courage to fight a war but it also takes courage to admit that wars can't be won with the current apparatus and although support for "the war" has blipped up, that reflects I suspect more the patriotic urge to get behind the troops than an honest assessment of where the Afghanistan campaign is going.