Hermiz Shahen doesn’t know what to feel. “We have nothing left in Mosul,” he says while digesting Foreign Minister Julie Bishop’s announcement that visiting his home town is now an illegal act. A Melburnian these days, Shahen hasn’t seen Mosul since 1981, as there have always been compelling reasons not to go back. The latest is the Islamic State’s seizure of the city and subsequent ultimatum to the mostly Christian Assyrian minority – leave, convert, pay tribute or die. Most chose the former, and so tens of thousands of these indigenous inhabitants of the Nineveh Plains were cast adrift from their ancient capital.

As the deputy secretary-general of the Assyrian Universal Alliance, Hermiz Shahen has to deal with these refugees on a daily basis, and last week was particularly busy. If exiling Assyrians from the banks of the Tigris was not enough, the IS got to work eliminating their historical presence as well, using sledgehammers to obliterate the false idols held within Mosul museum, pounding millennia-old artefacts into dust.

“What remains of our heritage, destroyed by such animals?” Shahen laments. Even that wasn’t the worst news, however, with the desecration of world history superseded by the kidnapping of hundreds of Assyrians. The fear is they will suffer the same fate as the Coptic Christians abducted and beheaded in Libya by IS militants. Nineteen of the captives have since been released, offering a glimmer of hope.

The conquest of Mosul by the IS and the Iraqi government’s impending counteroffensive are why Bishop has marked the city as the second “declared area” under powers granted by the Foreign Fighters Bill last year. The caliphate’s heartland of Ar-Raqqah in Syria was the first, and, just as in that case, on Monday Australians were given less than 24 hours’ notice to leave Mosul district or face a penalty of up to 10 years’ imprisonment, unless able to prove their presence is “legitimate”. The unprecedented step of making it a crime to simply be somewhere is to make it easier to arrest Australian IS fighters should they ever return, but the laws can apply to anyone.

Shahen confirms to me that Khamis Gewargis Khamis, a Melbourne man revealed by the ABC to be serving with the Assyrian militia Dwekh Nawsha, is based at the town of Baqofa, only 30 kilometres from Mosul city. Khamis had to make a tough call: stick with his wife, children and comfortable Australian life, or go and defend the relatives he left behind when he emigrated. He chose the latter, and while he intends to come back soon, Khamis has acknowledged there may be consequences, and not only if he ventures into Mosul district. Geography aside, Khamis might fall foul of the ban on fighting with non-state militia, broadened via the second tranche of national security legislation passed last year. Shahen is doing his best to give Khamis some wiggle room on this one, claiming the man is there to provide “moral support” to Dwekh Nawsha.

Khamis is by no means the only Australian who has joined the “counter-jihad” in Syria and Iraq. More than 90 Australians have joined the Islamic State or groups with similar ideologies, but the numbers joining Kurdish and Assyrian militias are unknown. At least two others are involved with the Kurdish YPG, including 28-year-old Ashley Kent Johnston, killed last week near the Iraq-Syria border when the vehicle transporting his contingent broke down and was set upon by IS militants. Multiple firsthand accounts claim Johnston leapt out of the vehicle to distract the enemy in order to give the others a chance to escape. The former Australian Army reservist had no ethnic ties to the Kurdish people, and is understood to have joined simply because he thought their struggle a noble cause.

Had he survived and returned to Australia, Johnston could have faced decades in jail. In October last year Attorney-General George Brandis warned that any Australian fighting for the YPG would face prosecution under the Crimes (Foreign Incursions and Recruitment) Act, with a maximum penalty of 20 years’ jail. Siding with the YPG is more complicated than siding with Dwekh Nawsha, as the Kurdish group is affiliated with the Kurdistan Workers’ Party, a proscribed terrorist organisation. Kurdish Australians are campaigning to have the terrorist status lifted, claiming the Australian government only maintains the listing for geopolitical purposes.

The other Australian involved with the YPG is former Northern Territory Labor president Matthew Gardiner, who left behind his job, wife and children in January to join the Kurdish cause. The 43-year-old former soldier was reported by the ABC to be in the same area as Johnston, but in a medical support role rather than direct fighting. When Labor supported the passage of the Foreign Fighters Bill through both houses of parliament, they surely never imagined it would come back to bite one of their own. Nevertheless, speaking at the time of Gardiner’s disappearance, Opposition Leader Bill Shorten was resolute: the former union heavyweight had made a mistake.

The Attorney-General’s Department issued an unequivocal statement on the matter of Australians wishing to join Kurdish forces, noting they are not the legitimate fighting force of Iraq. “Do not participate in the fighting as it only contributes to the suffering and puts you and others in mortal danger,” the statement read.

If the efforts of Kurdish forces to halt the advance of the IS only contribute to the suffering, it is curious then that the Australian government is actively arming them, as per the controversial decision last year to sidestep the Iraqi government and provide weapons directly to the Kurds. Amin Saikal, director of the Centre for Arab and Islamic Studies at the Australian National University, argues the government should only provide armaments directly to the Iraqi government, with strict controls in place.

“The Australian government is supplying arms to the Kurdish Peshmerga who provide these people with weapons,” he says. The Peshmerga routinely fight side by side with the YPG, and armaments and supplies are frequently shared.

Ben Saul, professor of international law at the University of Sydney, argues that fighting with non-state forces ought not be an issue. “Australians certainly should never commit terrorism or war crimes against civilians in any conflict,” he says.

“Instinctively it may also seem desirable that ordinary Australians should stay out of foreign conflicts altogether.

“However, it is morally and politically incoherent for Western governments to say that Islamic State must be defeated, while at the same time those governments are not willing to provide enough military assistance to defeat it, and are counterproductively criminalising ordinary people who bravely, and at great personal risk, seek to stop what our prime minister calls the ‘death cult’ of Islamic State.”

With Australia deploying 300 troops to train Iraqi forces against what Prime Minister Tony Abbott has painted as an existential threat, it is no wonder some Australians have felt compelled to take matters into their own hands. Saul singles out the ban on travel to specific regions as a particularly concerning element of this strategy, circumventing as it does the criminal law convention that authorities should have to prove a person has actually done something harmful. The ban on Mosul will expire in three years, however the foreign minister has the power to renew.

According to Greg Barton, a professor of politics and international relations at Monash University, the travel restrictions are vital for national security, given reliable information on what happens in war zones is extremely difficult to obtain and that the threat of radicalised jihadists returning and making an attack on home soil is very real. He sympathises with Australians who are fighting against the IS, but says the best that can be hoped for is that courts show leniency in sentencing such people on return.

“I believe courts will handle the case differently depending on whether someone fought with Islamic State or whether they fought with an opposing foreign militia,” he says. “The intent and nature of the group is a significant factor.”

Barton notes that while the Kurdish militia have offered crucial resistance to IS advances, they also have their own agendas, and alliances in the region are “fluid and complex”. Greater autonomy for the Kurdish people is one of their primary goals, which would threaten the stability of the Iraqi state.

The Assyrian people have similar aspirations. The Assyrian Universal Alliance had a series of meetings with federal government and opposition figures in Canberra on Wednesday, including assistant minister for defence Stuart Robert and shadow foreign minister Tanya Plibersek. Shahen tells me he pushed for Australians volunteering to defend his people to be supported rather than arrested, but also advocated for the creation of a “protected region” for Assyrians in northern Iraq.“Otherwise, we will not exist in Iraq anymore,” he says.

As it stands, it would take Assyria and Kurdistan going one step further and assuming outright statehood before Australians serving in their militias would be fighting legally, greeted on return not as criminals but as fighters who took on the “death cult”.