In his book Getting our Way, subtitled '500 Years of Adventure and Intrigue: the Inside Story of British Diplomacy' (2009), former ambassador and career diplomat Sir Christopher Meyer says that there's always a trade-off between what we might want to achieve and what we can actually do. 

As a result, we're sometimes left holding our noses and putting up with something that we would very much like to change, because what might replace it is even worse.

Vladimir Putin has made a potentially game-changing intervention in Syria on the side of President Bashar al-Assad. He has been a long-time backer of the Syrian regime, for obvious reasons: Syria provides Russia with its only Mediterranean naval base and losing it would be a major blow.

Now, however, he's upped the stakes. He has described Assad's forces – by far the greatest killers of civilians, including women and children, in the whole theatre ­– as "the only legitimate conventional army there". He wants coordinated action against Islamic State and al-Qaeda and is prepared to consider launching airstrikes unilaterally against them if necessary. He is holding talks with President Barack Obama under UN auspices in New York to try to get him on side.

This is a scenario that illustrates with extreme painfulness the humanitarian and moral dilemmas of the Syria conflict. The Western powers allowed Syria to slide into anarchy because they couldn't stomach supporting the brutal Assad regime. At the same time they were terrified of arming the opposition in case they backed the wrong horse and ended up arming Islamist extremists.

At the moment they could have done something to tip the balance against Assad, they failed to do so. His forces had crossed the so-called 'red line' by using chemical weapons; called on to allow airstrikes aimed at making it impossible for him to do so again, the British Parliament, followed by the Americans, instead gave him permission to continue. Thousands have died in agony since then as Assad's forces have dropped mustard gas on them from helicopters.

The Russian line on military intervention in support of 'friendly' rebel causes has been absolutely consistent. Russia was opposed to intervention in Syria. It was against airstrikes against the Gaddafi regime in Libya and against Saddam Hussein's forces in Iraq. It was opposed to Western meddling in Egypt during the uprisings against Hosni Mubarak. In each case Russia was portrayed as an apologist for brutal tyrants. In each case it warned of the danger of unintended consequences and of the catastrophe of anarchy.

The stories which came out of Libya and Syria were stomach-churning and contributed to a massive pressure on Western leaders including David Cameron to do something – anything – to help. But what was done, in each case, was enough to break the country but not to fix it. The former head of Britain's armed forces, General Lord Richards, revealed last year that the Prime Minister had in 2012 rejected a "coherent military strategy" to take on the Assad regime which would in his view have seen the Islamic extremists "squeezed out of existence".

In the recent controversial biography of Cameron by Lord Ashcroft, former Tory party chairman Michael Ancram is quoted as saying that his actions had left the country "ungovernable... with vast amounts of weapons from Gaddafi's arsenal moved south of the border, arming Boko Haram". More collateral casualties are adrift in the Mediterranean and trekking across Europe in search of a country willing to take them in: if Libya were still a functioning state, there would be far fewer of them.

So were the Russians right?

It's too simplistic to say so. Vladimir Putin's actions in Georgia, in Crimea and in Ukraine have been indefensible. He is a friend to Russia, not a friend to global peace. And Russia is playing its own games in the Middle East, which have more to do with energy security and geopolitical advantage than with any humanitarian considerations.

But at the same time, there is a hard-headed realism about the Russian position from which Western leaders should be willing to learn. Good intentions have not resulted in good outcomes.

It is deeply ironic that the policies of liberal Western democracies that speak the language of human flourishing should have contributed to devastation on such a scale, while the policies advocated by a power that cares nothing for anything except its own advantage would at least have left many more people alive.

In sorrow it must be said: one of the hardest lessons of these dreadful years has been that sometimes, the truly Christian thing to do is to leave a brutal dictator in power, because what succeeds him might be worse.

Follow @RevMarkWoods on Twitter.