Although it goes against all my instincts, sending the SAS back to Afghanistan makes sense. What other path is there to peace?

For everything there is a season, the author of Ecclesiastes writes, a time for every activity under heaven. And in that thought I find some solace, because in reason weeks I have found myself coming to the conclusion that there is wisdom in sending New Zealand's SAS back to Afghanistan.

Yesterday the government finally announced the decision it made weeks ago – New Zealand combat troops would be sent back to Afghanistan. Over the next 18 months three rotations of 70 SAS soldiers each would be deployed.

It should have been the most difficult decision this government has to make this term and it should be a decision that has nothing to do with trade. I won't judge the personal integrity of Cabinet members on that first issue, but I fear that trade was indeed an issue.

I instinctively oppose war; it signals a failure of leadership and humanity. I am an idealist who believes that taking a stand contrary to popular opinion is one of the most powerful and influential acts a person or country can make. I accept the lessons of history that no-one ever really wins in Afghanistan, and I respect sovereign borders enough to question the start of this war, when America invaded without United Nations sanction.

Although there was an argument to be made for our sending the SAS in 2001 – after the UN sanction – as part of a global effort to unseat a heinous Taliban regime, there was no argument to justify its return on 2004 and 2005 when the US military strategy in its insane 'war against terror' had been revealed to be so hopelessly misguided. If it were my son in the SAS, I would not want him in Afghanistan given the growing risk around this month's election and I would not want him to put his life at risk for a corrupt government that is unlikely in the extreme to be able to hold together the country as it now exists.

And yet even as I have rehearsed those arguments, I have found the contrary arguments more and more compelling.

In an ideal world Afghanistan would never have been invaded; or at least the US and NATO troops would have withdrawn as soon as the Taliban had been removed. We would have accepted that deposing the Taliban was justified in and of itself, but that anything after that a waste of time and lives. Sadly, other choices were made.

Now we must deal with what is, not what we wish had been. The tragic reality is that foreign forces have remained and now have an obligation to lay a foundation for what comes next. What that may be is impossible to predict. We will not be able to impose what we want. Afghanis must decide their own future and all we can know for sure is that they will not choose a liberal democracy with strong border.

Yes, the presence of western troops in Afganistan gives succour to Islamic militants. But the fact remains that western troops are there. So the only questions that matter are how to stabilise the country and how and when we get out.

The only remaining argument against the SAS's return is that it will do more harm than good; that violence will only beget more violence. Yet experience in Iraq gives us reason to believe a short surge may at least ease the conflict in the short-term and our commitment is only for 18 months, by which time we should know whether Obama's new Afghan strategy is working.

Despite the obvious flaws in this plan to try and stabilise a country that has been "unstable" for centuries , the alternative – a failed state, tribal warfare, unrestrained religious oppression, a resurgent Taliban, religious wars that spill over into Pakistan – is worse. For all our efforts those woes may yet come to pass, but surely we must do all we can to avoid that.

Those advocating non-involvement by New Zealand and immediate withdrawal by US and ISAF forces must either offer an exit strategy that is both instant and orderly or be willing take responsibility for the death and mayhem that follows. Because I can't envisage the former or do the latter, I can't oppose the government's decision. The least worst option is that foreign forces do what they can to stabilise the country before leaving over the medium term.

The political reality is that every country with soldiers in Afghanistan – and let's not forget that includes Australia, Norway, Sweden, Canada and Belgium – are all looking for a way out. The timing will be everything.

President Barack Obama has said as early as five months ago that he was working on an exit strategy. Just last week he again stressed the importance of Afghan personnel taking over the running of the country. He is talking of a "new phase" in his strategy after the Afghan elections in nine days' time.

Obama has also made it clear that America's policy on Afghanistan is now hand-in-glove with his policy on Pakistan. And thanks goodness. Between them, those two countries are the greatest threat to world peace that we currently face. We cannot risk chaos there; and when I say 'we' I mean especially New Zealand. If we care about a nuclear-free world, we must care about Pakistan's nuclear arsenal and who controls it.

So the core issue is how to retire those ISAF and US troops without the house of cards collapsing behind them. And that is a problem we have a responsibility to help solve.

It is precisely because we have sent troops in on three previous occasions that we are right to send troops back in now. It is, in part, our mess. We must play our part in cleaning it up. Only then can this time of war become the time of peace that we all long for.