IS IT just me, or do I detect more sniggering, restless foot-shuffling and unscripted voiceovers from the audience than is usual when the recruitment advert for the Royal Marine Commandos is screened at the cinema? Located on some South Pacific or Asian shore, the first character in the frame is our villain, a psychopathic-looking native with an oil-slicked and pigment-daubed body who is screaming in an incomprehensible, warlike tongue. Out from below a tropical bush creep our heroes, the Marines, the professionals employed by HM government to protect us all from miscellaneous nutters in foreign parts.

This advert is in a different league of ambition entirely from the plodding "Army - Be The Best" adverts that showed teenagers enduring borderline sado-masochistic survival exercises. At least they had an air of reality about them. This Marines advert is positively cinematic by comparison, if unreconstructed - a sort of Rambo versus idol-worshipping cannibals from Hollywood central casting circa the 1930s, directed by Ronald Reagan, and co-funded by Fox News. Unapologetic propaganda for the UK military project, it should come with a statutory warning, something like: "Joining the Royal Marine Commandos, or any other branch of HM Forces, could cause you to be killed, maimed or enlisted in some morally bankrupt war that you do not understand or don't agree with."

Still, the advert will doubtless appeal to the sort of young man who goes in for the Zoo magazine Man Of The Year competition currently advertised on the Royal Marines website under the banner "Are You Man Enough?". Win this competition and you net £3000, an iPhone, laptop, plasma screen TV, limited-edition Adidas trainers, digital camera and more. You also get to enjoy "not only the bragging rights of being the hardest man in Britain, but a once-in-a-lifetime experience of flying in a jet!". Zoo magazine apparently needed a "measurement of macho". Logically, it chose the Marines.

I'm not surprised that teachers have issues with this blatantly one-sided, rather reckless propaganda. After all, they spend their working lives trying to calm down aggressive young men who want to run around attacking people. This week, the National Union of Teachers voted to "support teachers and schools in opposing Ministry of Defence recruitment activities in schools that are based upon misleading propaganda".

The union also noted that the armed services concentrate their "awareness-raising" efforts in schools in deprived areas - in Wales, the army's own figures reveal 50% of its careers sessions had been thus targeted. Kids with few prospects have always been the prime recruiting base for the military.

The NUT can expect a neutron bomb-load of shit to be dropped on its heads for its efforts. The "Support Our Valiant Lads" army will be out in force, all the old, posh generals and toadying, lickspittle defence spokesmen who get wheeled out to talk about the courage of our armed forces, the debt of honour we owe them and the grievous body blow that will be dealt to recruitment as a consequence of this decision.

You have to admire bravery in the service of others, naturally. But there are other ways to demonstrate that bravery, such as joining the police, the fire service or mountain rescue squads.

And why does being in the armed services automatically make you a hero? Most recruits enlist for familiar, pragmatic reasons. Those born into the brigadier classes are more or less guaranteed a swift promotion to some cushy, elevated rank. Candidates who lack the qualifications for other jobs, who crave risk-taking and adventure, and yearn for the laddishness of the mess, are captivated by the armed forces. The army promises them "a lifetime of reward", full of "excitement, travel, opportunity". It's the only way some people are ever going to see a competitive pay and benefits or get a training, let alone qualify for subsidised accommodation and food, free medical and dental care, discounted rail travel and subsidised childcare. If I was facing a life stacking shelves in Tesco, I guess I'd be chuffed that the armed services wanted to send me off on a free helicopter ride.

But where's the balance? Maybe I missed it, but clicking on the armed forces recruitment websites, there's nothing to suggest that a career in this area has any downside, such as being blown up in Basra, or getting stuck on some God-forsaken base in Helmand province, Afghanistan, risking life and limb in an unwinnable war. This is the courageous point the teachers are making.

Why is this courageous? Because the armed services have always been a sacred cow, beyond criticism. Civil society is expected to silence political or moral objections when confronted with service personnel in uniforms. This is jingoistic nonsense.

We can't blame young people for being sucked into the services, but when they are sent to fight in useless wars, we should keep saying so. Above all, we should never stop challenging the politicians who sent them there in the first place.