When, tomorrow, Labour MPs rebel, and when Liberals and Nationalists dissent, they will have no shortage of arguments on their side. Certainly, they will have several more points to hand than the government in the debate over Trident renewal.

An administration expecting us to believe it decides multi-billion-pound expenditures on the basis that "you never know" is not rich in ideas, exactly. Ministers retreating to this, as it were, defensive position, have left the field clear for every opponent. It's bad politics and poor government, but since when did nuclear weapons have much to do with either? Not in 60 years.

The critics have their moral case, more or less unimpeachable. Just how do you defend weapons of mass destruction? Others will make a strategic argument. The world is threatened in any number of ways, they will say, but just which of those threats is, or is likely plausibly to become, nuclear?

Most MPs could, meanwhile, draw up lists of things urgently needed in their constituencies. This is neither petty nor parochial. It is the duty of parliamentarians to keep watch over the public finances. The government claims that Trident renewal will require £20bn. Organisations such as Greenpeace say government ignores the running costs of the system over its projected lifetime. They mention £75bn.

Whoever is right, many billions are at stake. One of them, at least, has already been spent rebuilding the Aldermaston establishment for the sake of a weapons system over which, this morning, "no decision has been made". Yet invoke schools, houses, hospitals, child poverty, transport, pensioners, whatever: MPs are entitled to wonder about the rush to invest in missiles.

Then there are those, finally, who remember our sworn commitments under the nuclear non-proliferation treaty. This is supposed to be one of our international obligations, but the government will not release the legal advice it has received. Even Whitehall lawyers find it hard to talk their way around blunt statements forbidding the transfer of nuclear devices from one state (the US) to another (Britain).

Make all these points and you have said some powerful things. But what have you really said? The government will win tomorrow, no doubt, thanks to the payroll vote (with a couple of minor exceptions) and the Tories. Not morality, not common sense, or prudence will prevail. A version of patriotism, a calculation as to future British influence and status in the world, will win. Other arguments carry more historic weight, but this is one that matters. How to change the minds of the nuclear armers?

If that cannot be done, we go on preaching to the converted, to the already-convinced abolitionists and to people who listened, astonished, to the fable of Iraq and WMD. In other words, we remain where we have been for decades, sometimes remembering the days when the Labour Party was unilateralist, more often recalling how Labour behaved when election became possible. Labour is not the practical, political problem.

David Cameron's efforts to change his party are well-known. The efforts, indeed, are perhaps the only things most people know, and then vaguely. Quite how radical Cameron is prepared to be remains a mystery. Quite how prepared his party is for soft-hearted radicalism remains to be seen. But ask the question, in any case: what would be a respectable Conservative case for nuclear disarmament?

Try this: for every £100,000 wasted on Trident renewal, a British service person will be put at risk. The transaction is more or less straightforward: billions earmarked for the next generation of unusable missiles while the army, reduced to barely 100,000 souls, attempts to fight two wars simultaneously, taking mounting casualties as it goes. What's patriotic about that?

What's patriotic about the ceaseless force rotations, the lack of body armour, the rotten boots, the duff radio systems, the lack of helicopters and air support, the vehicles without worthwhile protection, the failure even to get food through to troops under fire for days in Afghanistan? The stories have come and gone, each met with the glib reassurance that the forces will get "whatever they need". Sooner or later.

What's patriotic about stinking barracks and decrepit family accommodation? What's patriotic about pay and pensions miserable by any standard? And where's the patriotic pride in failing to provide the injured and the maimed, the scarred in body and mind, with decent medical services?

Cameron would promise, no doubt, that his government would tolerate none of this. He seems to say, though, that the Iraq and Afghanistan "commitments" should be maintained while he leads his party through the lobby to vote for Trident renewal. It doesn't add up. Britain is already Europe's biggest spender on defence, and fourth - though trailing by a large margin - in the world. Yet still our generals signal frantically that their army cannot cope. It makes no sense, and does no service to the defenders or the defended.

My perspective, you may have noticed, is not a Tory perspective. Iraq and Afghanistan are, respectively, illegal and suicidally illogical. Trident is a working definition of lunacy. Nevertheless, I'd like to hope - and even Tony Blair shared the hope, in the early days - that young people from these islands might no longer die in wars. We can all hope.

If I had to strike a political deal with Cameron and the Tories, however, I'd say this. Have your flags. Let's agree, nevertheless, that in an ideal world Britain's forces could do an honourable job of work for the UN. Let's agree that some of that world is liable to be dangerous, especially if we cannot bear another Srebrenica. Let's then agree that it is wrong to ask youths to fight without allowing them a fighting chance. So where does that leave Trident, and Tory patriotism?

Trident has more to do with the self-esteem of politicians than with Britain's defence needs. Most of those who will vote with the government tomorrow know as much: it's Tony's wish, his way of binding his successor. But why should Cameron agree? Simply to avoid being painted by the armchair heroes of new Labour as soft on defence? If half of what slips through from the soldiers in Afghanistan is true, real martial malleability involves boys in the middle of nowhere fighting for their lives.

Stupid wars and Trident missiles have no immediately obvious connection. I favour neither. I'm suspicious, too, of patriotism and people who need to talk about it. For all that, I would have thought it incumbent on a Conservative Party, of all parties, to explain how it would best defend the realm or, as the jargon has it, reconfigure the defence establishment. Simply to ape Blair is neither novel nor, given the blood and treasure at stake, particularly patriotic.

It's not much of a slogan, is it? "Support Our Boys - Lease Trident D5 from an Unreliable Ally and Fix the Radios Another Day." Cameron needn't take my word for this. He should not ask for a briefing from compromised MoD civil servants, above all. He should make no inquiries of admirals and air-marshals, who always get all the best toys.

Ask the generals. Then the officers. Then the squaddies. Then the families. Then ask if Trident is a Tory policy worth defending.