Attorney-General Christian Porter finds it "inconceivable" that a future federal government would abuse the much-expanded powers that his Government wants to give itself for calling out the Army for domestic purposes within Australia.

Requests for military backup during terrorist attacks would become easier under a shakeup of Defence "call-out" powers introduced into Federal Parliament in late June.

The changes would also allow the Australian Defence Force to be pre-authorised to respond to threats on land, at sea and in the air, and expand the military's powers to search, seize, and control movement at the scene of a terrorist incident.

But again, we are assured by the country's chief lawyer that it's "inconceivable" these powers would be misused to send troops out onto our streets.

Still it's worth considering how often we have been told by the Government that there is a difference between the wording of its laws and how they will be implemented.

Just last month it was that the police won't be able to access our My Health Record data without a search warrant. So why did the legislation explicitly give them that power, since (wisely) taken away.

When protests turn violent

Anyway, what's the worry here, we're only talking about the circumstances in which the Australian military will be permitted to shoot at, well, us. Yes, they would be constrained to using only reasonable force, but the issue here is the possibility they might be used in a domestic policing capacity — in other words, against our own citizens.

Our problem here is not the risk of Mr Dutton declaring martial law and putting certain people of his choosing in internment camps, although we should be concerned. ( ABC News: Ian Cutmore )

What I find inconceivable is the image of armed troops firing upon peaceful protesters in the streets of an Australian city. And yet there it is in my mind.

It's an image that may never have occurred to the good citizens of Northern Ireland until that "bloody Sunday" in 1972, when the British Army shot dead 13 unarmed protesters on the streets of Derry.

Or to the people of Amritsar, when troops of the British Indian Army fired on a large crowd of unarmed people, killing several hundred. Now, that was a fair few years ago, but it no doubt lives large in the memories of the relatives of those Punjabis killed, if not the entire and sizeable populous of India. In fact, according to the Encyclopaedia Britannica:

It marked a turning point in India's modern history, in that it left a permanent scar on Indo-British relations and was the prelude to Mohandas (Mahatma) Gandhi's full commitment to the cause of Indian nationalism and independence from Britain.

But consider this more recent (and local) example: in 2012, a protest rally in the Sydney CBD against an anti-Islam movie turned violent, and the NSW Police responded with heavy force. It was deeply unpleasant for all sorts of reasons, with ironically much in common with the anti-Muslim Cronulla riots of 2005 or the Reclaim Australia rallies of 2015.

In those instances, too, it was the job of the police to deal with what was extremely violent civil unrest — arguably, a national security threat.

I mention these examples, because in future it may not just be the boys and girls in blue taking to the streets when the rioting begins; the Army might be there as well — or instead.

Inconceivable, of course but, under the amended law, 100 per cent possible.

An over-reach that found support

The existing call-out law in the Defence Act was created in a rush ahead of the Sydney Olympics, and it was controversial then. Lawyers and civil liberties groups said at the time it was an unnecessary over-reach that would fundamentally change the role of the military. However, Labor supported it all-in, meaning there was no effective opposition.

Now call-out powers are being ramped up again, as a direct response to the debacle of the Lindt Cafe siege and the received wisdom that the Army's involvement on that awful day would have produced a different result.

That may be, but in fact the NSW Government could have asked the Army to step in under the current law.

And any time a government rushes to impair our freedoms claiming justification from a single incident, it's time to wonder what's really going on.

Looming large over all this is the figure of our Home Affairs Minister, Peter Dutton.

What will the amendments do?

Since having ASIO, the AFP and other security agencies added to his already quasi-militarised Border Force in a new super-department, Mr Dutton has taken the central role in the seemingly endless rollout of national security laws.

All the while, he's dished up dire warnings of what will befall us if we don't keep giving him new powers to defend us from ourselves.

The Defence Act amendments will do a lot, but here are the highlights:

1. The threshold for the Federal Government to send in the troops will change from being only when the relevant state or territory government is not, or is unlikely to be, able to do the job, to merely being satisfied that the Army's presence will be likely to "enhance" the ability of the police. Which, obviously, it will. They have tanks. 2. The Government gets a new power to make "contingent" call-out orders, meaning that it can decide that certain types of hypothetical circumstances will automatically trigger the call out power if they occur. 3. The soldiers will have essentially unlimited powers to search people and places, detain people, require them to answer questions and produce ID. Much more power than the police have. 4. And the pearl in the oyster: currently only the Prime Minister on his own, or the Attorney-General and Defence Minister acting together, can exercise the call-out power. Now either of those two Ministers will also be able to do it in combination with any of the Deputy PM, Treasurer, Foreign Affairs Minister or the Minister for Home Affairs.

Democracy is founded on separations of power

Our problem here is not the risk of Mr Dutton declaring martial law, although we should be concerned about the amount of power this Minister already wields.

Our focus should be closer than that. If this law passes, the Federal Government will have acquired a wide-open power to permanently change this country's social-legal compact, in a devastatingly anti-democratic way.

Democracy is founded on separations: church from state; legislature from executive from judiciary; and military force from domestic order.

The existing call out law blurs that last separation. The amended form will break it altogether.

It's no small thing. The only proper role of the military forces is to protect the national interest in extremis; it should never be used to perform the work of government.

This principle is an old one, enshrined in both the US and Australian constitutions.

In the US, the Posse Comitatus Act was passed specifically to stop the Federal Government from using the Army to police elections in former Confederate states.

Section 119 of our Constitution says that the Commonwealth must protect the country from invasion and, if asked by a State, "against domestic violence". That is the limit of its power, and it may well be that the call-out law is unconstitutional to the extent that it doesn't require state requests.

But the point is the intent: domestic policing is for the police, and the Army doesn't get called in except as a last resort.

The Army should only ever be called out domestically if the nation's security is at existential risk. ( Commonwealth of Australia, Department of Defence )

Howard started a trend

The blurring of this distinction began with the Howard Government's co-opting of the Navy in anti-asylum seeker operations off-shore, massively expanded by Tony Abbott.

The Army should only ever be called out domestically if the nation's security is at existential risk. This may be in the instance of, for example, a devastating terrorist attack.

But, in introducing the amending bill, Mr Porter was explicit as to what the Government has in contemplation:

Today, it is most likely that domestic terrorist attacks will be carried out by individuals or small groups…using simple methodologies – knives, edge weapons, guns, cars – and could be over in minutes.

If so, what need or use for the Army? If our police are incapable of dealing with this type of terrorist attack, then the problem is their resourcing, training or competence. And they can already call on the Army for help if they need it.

The amended law will, beyond argument, allow the Federal Government to call out the Army, whether or not a State Government wants it, to respond to an incident of mass civil disturbance — such as the 2005 or 2012 Sydney riots. Do you want the Army there for that?

Michael Bradley is the managing partner of law firm Marque Lawyers.