But he now wonders if he is in some sort of different category. His country has told him that if he comes home, home could be a jail cell for five years.

"I've been telling people how proud I am to be an Australian, but now I don't feel the same way," he says.

People in India have been mocking him, saying "your government doesn't want you".

"It's pretty horrendous," he says. "I always felt like I was accepted. I feel like we are being treated differently from other citizens."

He went to India to get married. His and his bride's return was booked for next Tuesday, but the flight was cancelled.

On Monday, the Federal Court will examine the government's block on Australian citizens returning to Australia. The implied question is: how much value is there in the words on the Australian passport about the bearer "passing freely without let or hindrance"?

The Prime Minister has said flights will resume, but the court hearing will indicate how much protection citizens of Australia have. It's about the wider principle.

"What we are seeing is how vulnerable our rights and liberties can be to government encroachment," says Professor Tim Soutphommasane of Sydney University (and formerly of the Australian Human Rights Commission).

"We don't have a bill of rights or a constitution that explicitly says anything about many of our basic rights. We don't have a political culture that values citizenship.

"It wasn't until 1949 that citizenship was even a legal category in Australia. Prior to that, people thought of themselves as British subjects, not as Australian citizens."

He says citizenship is about much more than just having a passport.

"We don't like to think about its political meaning. But the current situation reminds us citizenship is fundamentally about membership," he says.

"It's a statement about who belongs in our community, and about who we are. Unfortunately, the criminalisation of citizen returns from India not only undermines the value of national solidarity, it sends a signal that not all citizens are equal in the eyes of government."

Lawyer Dr Sangeetha Pillai of the Kaldor Centre for International Refugee Law at the University of NSW agrees.

"The citizen owes allegiance to their nation, and the government owes protection," she says.

As the Department of Home Affairs puts it: "Becoming an Australian citizen means that you are making an ongoing commitment to Australia and our shared values. It is also the beginning of your formal membership of the Australian community. It is the step that will enable you to say 'I am Australian'."

But the permanence of citizenship was diluted by the Australian Citizenship Act 2007, which says that citizenship can be revoked "if the minister is satisfied that it would be contrary to the public interest for the person to remain an Australian citizen".

So far, the reasons cited for cancelling Australian citizenship have been the committing of serious crimes, particularly terrorism - but the clause is vague and capable of wider interpretation.

Australia does have a written constitution, but it is very limited. It was written at the time of Federation to lay out the relationship between the Commonwealth government and the states and territories. It doesn't set out citizens' rights. Much of Australian law has grown up through the centuries as English law and then Australian law, with courts and parliaments setting new laws.

When it comes to Monday's legal challenge in the Federal Court, Dr Pillai says "there is no clear path to success".

But there are two possible routes. The first is that the challengers to the government will argue that there is some sort of implied legal protection for exiled citizens.

"Due to the deep links between citizenship and the right of return, it has been suggested citizens may have an implied constitutional right to enter Australia," Dr Pillai says.

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Legal scholar Professor Kim Rubenstein of the University of Canberra agrees with this argument.

"A constitution exists to put limits on those in power," she says. "What is the value of having those limits, if you can keep out the people who are meant to be protected by those limits?"

The second strand of the case against the government is that it has misapplied biosecurity law. The aim of such law is to keep threats to Australian health or agriculture out of the country - but it has to be applied carefully, and only when other options are exhausted.

The ban was invoked by ministerial decision, and not after any parliamentary decision. A minister does have such a power, but there are tight constraints on when he or she can use it.

Two of the conditions for invoking the Biosecurity Act 2015 are "that the requirement is no more restrictive or intrusive than is required in the circumstances" and "that the manner in which the requirement is to be applied is no more restrictive or intrusive than is required in the circumstances".

The big question will be: could the government have protected Australia in a better way than by shutting out 9000 citizens? The lawyers will have this debate, focused on the phrase "required in the circumstances".

Dr Pillai says better ways than the ban were available.

"The federal government could protect more people in Australia and abroad if it worked to bring citizens home while devoting more resources towards strengthening the quarantine system," she says.

Professor Rubenstein is also reasonably bullish.

"I think there are very strong arguments that the determination is unlawful (and also the ban on people leaving)," she says.

"We will now see what the Federal Court thinks."