We're told that dropping bombs on Syria fulfils our legal, moral and practical obligations. But our refusal to learn from past experience guarantees the seeds of future wars are being sown by our approach to winning the current one, writes Michael Bradley.

So we're going to war in Syria. Not really war, we haven't technically been at war with anyone since World War Two.

But we will be dropping bombs on Syrians. The decision has three dimensions: legal, moral and practical. The Government's rhetoric glosses each of them as boxes that tick themselves.

The rolled up logic goes like this: Islamic State doesn't respect borders (so why should we); IS is evil; there can be no safety or security for the millions of displaced Syrians and Iraqis until IS is degraded and ultimately destroyed. Also, Obama asked us (not sure whether that goes in the legal, moral or practical box).

Law first. It is illegal in international law to engage in military aggression inside another country, unless the government there has asked you in, or the UN Security Council has authorised it, or in self-defence.

The Syrian government is Bashar Assad, who has been quite dedicated to the task of murdering his own people. Since he is supported and armed by Russia, UN consent is off the table. Assad is happy for the US and friends to come in and bomb IS, but he isn't going to say so.

That leaves self-defence. We're in Iraq, bombing IS there, at the Iraqi government's request. The argument is that IS is crossing the border freely and using Syria as a base for operations in Iraq. As part of our participation in Iraq's self-defence, we need to cross over too and hit IS where it hurts.

Law is changeable; international law very much so. The traditional rules for when it's OK to invade were written at a time when global-scale terrorism wasn't in contemplation.

The precedent for an expanded self-defence justification was set by the invasion of Afghanistan following 9/11, when the US and allies went in to destroy Al Qaeda. The legal theory, that it's OK to reach inside the borders of another country to get at terrorists who are being harboured there by a rogue regime, has a lot of merit. The Taliban was actively hosting and protecting Al Qaeda, so it made sense.

The precedent doesn't work in Syria, however. Assad isn't harbouring IS, he just doesn't control most of his own country and can't get rid of them (apart from being more personally focused on killing civilians). To justify going into Syria, the legal principle has to be further expanded to encompass going after terrorists who are hiding out in a country whose government doesn't support them but isn't asking for help. That's a rather more slippery slope and a potentially problematic precedent.

A legal case could be made for this intervention in Syria; it's troubling that the Australian Government has not bothered to properly argue it or to bring the question before Parliament. This lazy approach is what led us into Iraq in 2003, illegally and disastrously.

The moral justification is at first glance clearer: IS is a murderous group exemplifying all the worst traits of humanity, and stopping it is a moral obligation. Tony Abbott's comparisons of IS with the Nazis are as inapt as they are offensive and bone-stupid, and it'd be really nice if he stopped doing that. Nevertheless, IS has no redeeming features and must be fought.

The problem is that the argument presupposes that IS is a self-created entity. The truth is that we are partly responsible for its emergence, by invading Iraq and destabilising the entire region.

The Middle East is a long-term mess, not anyone's fault entirely, but if we keep approaching each disaster with the perspective of, "Oh look, isn't that dreadful, let's shoot some bad guys", instead of acknowledging that what's happening now is part of a continuum in which we are deeply enmeshed, then we'll just keep making it worse.

That's not an argument for leaving IS alone; it's an argument for honesty as a precondition to the assertion of morality.

Finally, practicality. Abbott says we must degrade and ultimately destroy IS. What he doesn't admit is that we can only ever achieve the first part of that equation, and that only temporarily.

There are two elements to this. First, is it possible to achieve the military aim of permanently degrading or destroying an armed insurgency from the air alone? Secondly, can you destroy an ideology?

Both these questions are answered by history. No war has ever been won from the air. Ground forces are always required, one way or the other. A lot of IS fighters have been killed, and maybe eventually it can be fought to enough of a standstill that the remainder give up the cause. The cause will still exist. Our refusal to learn the lessons of past experience guarantees that the seeds of future wars are being sown by our approach to winning the current one.

If IS is the bastard child of Al Qaeda, it's not pleasant to imagine what the grandkids are going to look like.

Michael Bradley is the managing partner of Marque Lawyers, a Sydney law firm, and writes a weekly column for The Drum. Follow him on Twitter @marquelawyers.