Almost two weeks after the story was broken by the ABC’s Foreign Correspondent, the fate of Ben Zygier — also known as “Prisoner X” and various other aliases — remains mysterious. But we know enough to know that it raises some difficult questions.

Zygier fell foul of the Israeli authorities as a result of something he did while working for Mossad, the Israeli spy agency. It appears that at the time he had some contact with ASIO, Mossad’s Australian counterpart, at a time when Australian-Israeli relations had been strained by the discovery that Mossad had used fake Australian passports in one of its operations.

The rest is conjecture. But even if the fairly natural conjecture that Zygier was imprisoned for something he said to ASIO turns out to be false, it’s been enough to set off a debate about the problem of dual citizenship.

For centuries, Jews have been the victims (not the only ones, of course, but the most widespread) of allegations of “dual loyalty” — that although they purported to be loyal citizens of the countries in which they lived, their primary loyalty was to “world Jewry” and its “sinister conspiracy” against Christian civilisation. (Catholics got a lot of the same treatment for being allegedly loyal to the Pope rather than their own governments.)

So the allegations against Zygier touch on a very raw nerve. Gabriel Sassoon in Haaretz refers to “Dreyfus-style allegations” and “a canard almost exclusively and reflexively leveled at Jews”. Critics such as Joseph Wakim counter that “we cannot turn a blind eye to the human traffic and ‘rites of passage’ between Australia and Israel”.

This all makes it important to be very clear that the problem here is not some abstract idea of “dual loyalty” but the very specific question of dual citizenship. Zygier got into trouble not because of his religion or ethnicity or national origin, but because he was simultaneously a citizen of two different countries, whose interests were not identical.

Not so very long ago, dual citizenship was an unusual condition. There was even a European treaty to try to minimise it, the 1963 Convention on the Reduction of Cases of Multiple Nationality. As I put it a 2011 article:

“In the classical model of citizenship, dual citizenship was rare and anomalous. Citizenship was inherited from your father; on the rare occasions it changed, it meant giving up your ancestral citizenship to acquire a new citizenship in the polity to which you (or more likely your parents or grandparents) had moved.”

Two particular factors have driven the move away from that model in the last half-century: greater equality of the s-xes, so that people now inherit citizenship from both parents, and the gradual disappearance of compulsory military service, which was the biggest reason to avoid conflicting obligations. More important than either, however, has been the march of globalisation, where people need and demand flexibility to move between countries without being hamstrung by archaic legal requirements.

In a globalised world, “citizenship” is on its way to becoming an anachronism. There are a handful of rights that we don’t want people to able to exercise in two different countries (voting, receiving welfare payments), but for most of the benefits of citizenship there is no reason why they should not be extended to anyone who wants to live in a country, and retained as they move around the world.

Nations now compete for the educated and the entrepreneurial; they no longer depend on a mass-conscripted infantry for their survival. Times have changed.

But what the Zygier case demonstrates is that our embrace of modernity has been incomplete. Our governments still have one foot in the feudal era, where “allegiance” meant an obligation to fight and die for your lord and master. Australia may have abolished conscription (although Israel of course has not), but we still have a law of treason and security agencies like ASIO to enforce it.

Zygier’s conflict was not (just) personal or emotional but legal and structural. He was in a situation where — at least hypothetically, and perhaps actually — he had specific legal obligations to two different countries, which could not both be satisfied. The second country happened to be Israel, and perhaps Israel’s difficult security situation made the problem more acute, but in principle it could have been anywhere.

That’s the problem that the world needs to address. As long as we care about “allegiance”, with all its pre-modern baggage, it’s not going to go away. Yet can we really imagine a world without the distinctive status of citizenship?