With Syrian forces reported to be moving on areas around Syria's second city, Aleppo, the cause of so-called liberal interventionism appears to be receiving a boost. "The regime has chemical weapons and is using them; we cannot stand by," goes the argument. Not wishing to frighten the horses with talk yet of "boots on the ground", we hear "arm the rebels" instead. Unless we do, says General Salim Idriss, chief of staff of the Free Syrian Army, who seems to command very few troops on the ground, those same rebels will not attend any peace talks.

The first question any sensible politician needs to ask is: "If we're doing this, with what kind of weapons shall we 'arm the rebels?' What can we provide over and above the more than $3bn of weapons supplied by Saudi Arabia and Qatar?" Let's assume that those "rebels" who are minimally militarily competent are not jihadists linked to al-Qaida who learned their trade killing British and American soldiers in Iraq.

Let's also assume, rightly, that jets, artillery and tanks are off the menu. These require years of training. What about "small arms", rifles, mortars and such things? A batch of past-their-sell-by-date British SA80 rifles will be unwelcome in a country already knee-deep in more suitable Kalashnikovs. What about anti-tank missiles? The trouble with more effective weapons, such as the UK's Javelin, is that they need extensive training by experienced soldiers to be useful. Those would be our soldiers.

The same applies for the far more dangerous question of anti-aircraft missiles, known as "manpads" in the trade (man-portable anti-aircraft defence systems), all of which require experienced handling. The US, Britain and other countries have made great efforts, but had little success, in trying to track down stray manpads in Afghanistan, Iraq and Libya. In Aleppo or elsewhere, these weapons may well take down a few MIGs or helicopters; the trouble is that they are even more effective against Airbuses or Boeings.

The next question, and the really uncomfortable one, is: "What if 'arming the rebels' has no effect?" The Syrian opposition knows very well that no "game-changer" weapons are on the agenda. The real objective of the anti-Assad forces is full-scale western military intervention. We need to understand that once we start down the road marked "arming the rebels", we are on a journey that will take us to "no-fly zones", and beyond.

Syria is likely by then to be armed with the latest, and highly effective, Russian missiles. A serving RAF officer recently told me that the Syrian air defence system was "layered and serious. We would take casualties." That means dead or captured British airmen. Our no-fly zone would of course lack UN backing as we have spent the last two years antagonising Russia. We will then hear talk of "safe havens" protected by whatever few thousand British troops can be spared from the baleful, sputtering Helmand campaign. A case-hardened US armed forces, backed by an equally reluctant President Obama, are not at all keen to get involved in another Middle East quagmire. They know that once again they will be doing the heavy lifting. We need to get beyond appeals to false analogies: "remember Bosnia" – the Bosnian Serbs had the support of clapped-out Serbia – or "what about Rwanda" – the killers had no external support at all. We need to be absolutely clear, and clear now, what exactly we are trying to achieve and whether we can in fact achieve it. In other words we need a clear strategy. The last 10 years would indicate that we are not particularly good at that.