First let's get one thing clear, Putin is not making a principled, humanitarian intervention against Islamic State.
Assad is Russia's ally in the region. The major disagreement between Russia and the West is Assad's place in the post-civil war Syria. Putin thinks it's Damascus, the west thinks Assad belongs in The Hague. Failure by the west to intervene left a power Vacuum into which Putin waded with his military. This served a number of purposes.
- It put Vladimir Putin centre stage in negotiations which allows him to present himself as someone who's made Russia a force once more in world affairs. Those handshakes with the American president are extremely important in the Russian Media.
- By deploying credible forces to the region Putin gains a seat at the table and earns a bargaining chip, potentially in return for the easing of Sanctions. This should be resisted.
- Helps secure Russia's southern flank, itself vulnerable to Jihadists
- It's a show of military strength - a rapid expeditionary deployment of forces at short notice. In doing so he's made a virtue of necessity: you cannot hide such a deployment 70 miles from the British listening station on Cyprus, so use it to distract from the ongoing destabilisation of Ukraine and demonstrate capability.
- Finally, most refugees aren't fleeing the theatrical murderers of Islamic State, but the desperate Assad regime, which is killing seven times as many Syrians as the "Caliphate". The refugees are therefore fleeing a war which Assad is at present losing, and probably would have already lost by now were it not for Russian support. The resultant refugee crisis weakens the EU, another Putin bugbear, so he's perfectly happy to prolong the Syrian slaughter.
The fact is Assad isn't fighting IS all that much, but is instead losing ground to moderate rebel groups in the south, Jabat al Nusra (the official Al Qaeda franchise in the region) and many others in the west. He's even ceded some ground to Hezbollah, in return for their military support. The Kurds, Hezbollah and JAN Islamists are the main opposition to IS. Most Russian actions appear to be against non-IS rebels too. The main purpose is to support Assad.
The main function of bombing IS is for Putin to further play to his supporters in the west's belief that "here is a man of action and a man of principle". Assad's regime is propped up. The refugees continue to split Europe, and western inaction exposed as weakness.
For the west's part, there's nothing that would solve many of our Foreign policy problems more than Russia getting sucked into an unwinnable war in the Middle East. By taking the best kit south, it would take pressure off Central Europe and Ukraine. It would cost Russia money it doesn't have, weakening them in the long run.
It's all breathtakingly cynical. We should not be persuaded by any of it. The Western powers had an opportunity to intervene in 2013 and earlier. Now it's too late. The Russians have made their play, and we (and above all the Syrians) must live with the consequences. If you take "Iraq" as a cautionary tale of going to action, Syria is a cautionary tale against inaction. Of the two, Iraq was basically a draw, and Syria is a catastrophic cluster-fuck that's strengthened one of the worst people in the world. Inaction appears to be worse.