What is worse? Locking somebody up for years, without trial, while you try to find proof he is a terrorist? Or killing somebody whose name you don’t even know because his pattern of behaviour suggests to you that he is a terrorist?

The first strategy, internment without trial at the Guantánamo Bay prison camp, was a signature policy of the George W. Bush administration. The use of drone strikes to kill suspected terrorists has become a trademark of the Obama administration. Yet while Guantanamo attracted worldwide condemnation, the use of drones is much less discussed.

It is hard to avoid the impression that US President Barack Obama is forgiven for a remarkably ruthless anti-terrorism policy simply because his public image is so positive. He won the Nobel Peace Prize for goodness sake!

Yet Obama’s free pass on drones may be running out. America’s expansion of this secretive programme is finally attracting legitimate criticism and concern — and not just from the usual civil-liberties types.

Kurt Volker, a former US ambassador to Nato for George W. Bush, asked recently in The Washington Post: “What do we want to be as a nation? A country with a permanent kill list? ... A country that instructs workers in some high-tech operations centre to kill human beings on the far side of the planet because some government agency determined that those individuals are terrorists?”

Volker’s diatribe reflects the moral uneasiness that many feel at the remote, computer-game-like quality of drone warfare. But, while drone strikes may make killing too easy and tempting, the remoteness of the method is probably the least coherent objection to the campaign.

Most countries would be delighted to find a way of minimising casualties among their own troops. And civilian deaths or mass casualties are just as likely to be caused by the methods of conventional warfare — such as a piloted aircraft or an artillery shell.

The more serious objection to drones is that they have blurred the line between war and assassination. Somebody suspected of plotting a terrorist attack on the soil of the US or the UK would be subject to arrest and prosecution. But if the suspects are in the tribal areas of Pakistan, they can simply be blown away.

While most strikes have been undertaken by the US military in recognised theatres of war, such as Afghanistan or Iraq, there is also a large covert programme of drone attacks in Pakistan, Yemen and Somalia run by the CIA. Some are aimed at known terrorist suspects, such as Anwar Al Awlaki, a radical Islamist with a US passport, who was killed in Yemen. Others are so-called ‘signature strikes’, in which unnamed suspects are targeted, based on their pattern of behaviour.

America argues that even signature strikes are precisely targeted and that civilian casualties are minimal. But that is disputed. A recent study by Stanford and New York University law schools endorsed the claim that between 474 and 881 civilians, including almost 200 children, have been killed by drone strikes in Pakistan.

One case — in which a meeting of tribal elders called to discuss a mining dispute was hit, killing 42 people — is now the subject of legal action in Pakistan and Britain. (The British are accused of providing intelligence to the US.)

The Obama administration’s legal justification for these strikes depends on a literal reading of the phrase ‘war on terror’. In a war, it is routine to attack concentrations of enemy forces. Thus, it is argued, is legitimate to attack Al Qaida forces in Pakistan. Yet many lawyers regard this argument as something of a stretch.

No war has been declared in Pakistan and the campaign is being conducted covertly, by an intelligence agency — not by the US military. The legal basis for drone strikes looks even more tenuous when they are conducted in Somalia, thousands of miles away from the battlefields of Afghanistan.

The niceties of international law are probably of little concern to many citizens, who are happy to be protected from terrorism and to zap ‘bad guys’. But the precedents set could come back to haunt the US and its allies.

During the presidential election campaign, this thought began to worry some members of the Obama foreign policy team. One recalls that “we realised that if we lost, we would be handing over an industrial strength killing machine to Mitt Romney”. Yet efforts led by the state department to introduce more rules and transparency to the drones campaign were effectively pushed back by the CIA and the Pentagon.

Now that Obama has been re-elected, it seems more likely that the drones campaign will be expanded rather than reined in. But the precedents set should still worry the US. Many countries — from Turkey to Russia and China — claim to be waging a war on terrorism. What if some of them follow the example set by America and decide to start eliminating enemies on foreign soil through the use of drone strikes? The technology involved is not hugely expensive or hard to master.

To make the spread of drone warfare less likely — and to prevent abuses in America’s own programme — drones need to be reclaimed from the realm of covert warfare. The CIA may relish its conversion into a paramilitary force. But wars should be fought by the military and openly scrutinised by politicians and the press. Anything else is just too dangerous for a free society and for international order.

— Financial Times