An image downloaded June 11 from the jihadist Web site Welayat Salahuddin shows militants of the Islamic State of Iraq and the Levant waving the trademark Islamist flag after they allegedly seized an Iraqi army checkpoint in the northern Iraqi province of Salahuddin. (Ho/Welayat Salahuddin via AFP)

British security services estimate that there are 500 or so U.K. citizens fighting with the Islamic State in Iraq and Syria. If you include the Brits fighting with other extremists groups, the number of British "foreign fighters" expands considerably. These people may have spent months or years being steeped in extremist culture and receiving military training, yet they are still British citizens. It begs an uncomfortable question: What happens when they finally return home?

The British government thinks it has found a workable solution to that quandary: Don't let them return.

On Friday, Prime Minister David Cameron announced remarkable new terror laws that sought to tackle Britain's foreign fighter problem. "We will shortly be introducing our own new Counter-Terrorism Bill in the United Kingdom," Cameron said in a speech in Australia. "New powers for police at ports to seize passports, to stop suspects travelling and to stop British nationals returning to the U.K. unless they do so on our terms."

It's radical thinking, but the concept of blocking the return of extremists appears to be catching on. Canada has already begun revoking the passports of citizens who travel to Iraq and Syria to join extremist groups. “I just don’t want to get into the numbers, but multiple cases," Citizenship and Immigration Minister Chris Alexander told the Globe and Mail in September.  Norway has mulled a similar tactic, while Australia has proposed tough new laws that allow them to jail anyone who has been to an area where terrorists have been fighting.

The logic behind the move is understandable. As the head of London's anti-terror police unit put it recently, it seems "almost inevitable" that a returning British citizen would try to mount attacks in the United Kingdom.

But by focusing on the threat, Western countries could end up ignoring the potential upside of the return of disillusioned jihadists.

While some foreign fighters in Syria and Iraq have gained infamy (the now-notorious Jihadi John, for example), other Westerners have clearly had a tougher time out there. Rita Katz, a terrorism analyst and co-founder of the Search for International Terrorist Entities Intelligence Group, today wrote a report that noted that many foreign fighters had begun asking hard questions about their lifestyle on social media. "How long will we remain here?" Katz paraphrased. "And what happens next?"

It seems likely that some of these people are simply not cut out for the hard lifestyle of a jihadist, but others may well have become disillusioned with the Islamic State and other extremist groups ideologically. As The Post's Griff Witte reported recently, many analysts in London are wondering whether foreign fighters who've had a change of heart could actually be useful for the British government.

“They've been sold a lie. They didn’t sign up for this sort of barbaric behavior, and now they want out,” Hanif Qadir, chief executive of the Active Change Foundation (ACF), an anti-extremist group, told Witte. Qadir himself had once traveled to Afghanistan and Pakistan shortly after the War on Terror began, enticed by extremists, but returned later after feeling that al-Qaeda and the Taliban were hypocritical.

“You can't look at these individuals as potential threats," Qadir said. "You have to look at them as potential assets.”

Some countries have tried this tactic. Denmark, for instance, has tried to integrate them, offering free psychological counseling and working to find them jobs or education. It's been a controversial tactic, but has produced some hopeful results so far.

The British government's proposed law does have some leeway that might allow British foreign fighters who pose no threat to return. According to the BBC, British citizens who had fought abroad may be given the option to give themselves up at the border. Depending on their situation, they might face prosecution, yet they also may get away with some form of supervision by British security forces.

However, at its most extreme, the proposed law also allows Britons who fought abroad to be banned from entering the country. While these bans will only last two years, they can be renewed indefinitely. In effect, these British foreign fighters could be made stateless. This could have some difficult repercussions for international relations and fit into a broader history of using statelessness as a punitive measure.

It's a double-edged sword. Cameron's proposed law may well provide security at home, at least temporarily. But a policy of exclusion could further alienate a minority who already feel dangerously excluded. And more worryingly, there seems to be little evidence that it'd help the global fight against the Islamic State and other extremist groups. Osama bin Laden had his Saudi citizenship stripped from him back in 1991, after all.