It's as if it's a habit they can't kick. Once again US, British and other Nato forces are bombarding an Arab country with cruise missiles and bunker-busting bombs. Both David Cameron and Barack Obama insist this is nothing like Iraq. There will be no occupation. The attack is solely to protect civilians.

But eight years after they launched their shock-and-awe devastation of Baghdad and less than a decade since they invaded Afghanistan, the same western forces are in action against yet another Muslim state, incinerating soldiers and tanks on the ground and killing civilians in the process.

Supported by a string of other Nato states, almost all of which have taken part in the Iraq and Afghanistan occupations, the US, Britain and France are clinging to an Arab fig leaf, in the shape of a Qatari airforce that has yet to arrive, to give some regional credibility to their intervention in Libya.

As in Iraq and Afghanistan, they insist humanitarian motives are crucial. And as in both previous interventions, the media are baying for the blood of a pantomime villain leader, while regime change is quickly starting to displace the stated mission. Only a western solipsism that regards it as normal to be routinely invading other people's countries in the name of human rights protects Nato governments from serious challenge.

But the campaign is already coming apart. At home, public opinion is turning against the onslaught: in the US, it's opposed by a margin of two-to-one; in Britain, 43% say they are against the action, compared with 35% in support – an unprecedented level of discontent for the first days of a British military campaign, including Iraq.

On the ground, the western attacks have failed to halt the fighting and killing, or force Colonel Gaddafi's forces into submission; Nato governments have been squabbling about who's in charge; and British ministers and generals have fallen out about whether the Libyan leader is a legitimate target.

Last week, Nato governments claimed the support of "the international community" on the back of the UN resolution and an appeal from the dictator-dominated Arab League. In fact, India, Russia, China, Brazil and Germany all refused to support the UN vote and have now criticised or denounced the bombing – as has the African Union and the Arab League itself.

As its secretary general, Amr Moussa, argued, the bombardment clearly went well beyond a no-fly zone from the outset. By attacking regime troops fighting rebel forces on the ground, the Nato governments are unequivocally intervening in a civil war, tilting the balance of forces in favour of the Benghazi-based insurrection.

Cameron insisted on Monday in the Commons that the air and sea attacks on Libya had prevented a "bloody massacre in Benghazi". The main evidence was Gaddafi's threat to show "no mercy" to rebel fighters who refused to lay down their arms and to hunt them down "house to house". In reality, for all the Libyan leader's brutality and Saddam Hussein-style rhetoric, he was scarcely in any position to carry out his threat.

Given that his ramshackle forces were unable to fully retake towns like Misurata or even Ajdabiya when the rebels were on the back foot, the idea that they would have been able to overrun an armed and hostile city of 700,000 people any time soon seems far-fetched.

But on the other side of the Arab world, in western-armed Bahrain, security forces are right now staging night raids on opposition activists, house by house, and scores have gone missing as the dynastic despots carry out a bloody crackdown on the democratic movement. And last Friday more than 50 peaceful demonstrators were shot dead on the streets of Sana'a by government forces in western-backed Yemen.

Far from imposing a no-fly zone to bring the embattled Yemeni regime to heel, US special forces are operating across the country in support of the government. But then US, British and other Nato forces are themselves responsible for hundreds of thousands of dead in Iraq and Afghanistan. Last week more than 40 civilians were killed by a US drone attack in Pakistan, while over 60 died last month in one US air attack in Afghanistan.

The point isn't just that western intervention in Libya is grossly hypocritical. It's that such double standards are an integral part of a mechanism of global power and domination that stifles hopes of any credible international system of human rights protection.

A la carte humanitarian intervention, such as in Libya, is certainly not based on feasibility or the degree of suffering or repression, but on whether the regime carrying it out is a reliable ally or not. That's why the claim that Arab despots will be less keen to follow Gaddafi's repressive example as a result of the Nato intervention is entirely unfounded. States such as Saudi Arabia know very well they're not at the slightest risk of being targeted unless they're in danger of collapse.

There's also every chance that, as in Kosovo in 1999, the attack on Libya could actually increase repression and killing, while failing to resolve the underlying conflict. It's scarcely surprising that, outgunned by Gaddafi's forces, the Libyan rebel leadership should be grateful for foreign military support. But any Arab opposition movement that comes to power courtesy of Tornadoes and Tomahawks will be fatally compromised, as would the independence of the country itself.

For the western powers, knocked off balance by the revolutionary Arab tide, intervention in the Libyan conflict offers both the chance to put themselves on the "right side of history" and to secure their oil interests in a deeply uncertain environment.

Unless the Libyan autocrat is assassinated or his regime implodes, the prospect must now be of a bloody stalemate and a Kurdistan-style Nato protectorate in the east. There's little sympathy for Gaddafi in the Arab world, but already influential figures such as the Lebanese Hezbollah leader Hassan Nasrallah have denounced the intervention as a return to the "days of occupation, colonisation and partition".

The urgent alternative is now for countries such as Egypt and Turkey, with a far more legitimate interest in what goes on in Libya and links to all sides, to take the lead in seeking a genuine ceasefire, an end to outside interference and a negotiated political settlement. There is nothing moral about the Nato intervention in Libya – it is a threat to the entire region and its people.