I DON'T know who David Cameron was speaking for when he lacerated the Russians and the Chinese at the UN General Assembly last week.

He certainly wasn't speaking for me. In his ill-tempered speech Mr Cameron emotively referred to "the blood of children" and came close to blaming China and Russia for the atrocities being committed in Syria by the Assad regime.

China and Russia have consistently blocked moves by the UN Security Council to put pressure on President Assad, the Syrian leader. Of course this man is an odious tyrant, and the crimes he is committing against his own people are inexcusable. But, as Vladimir Putin said in a dignified and calm response to David Cameron's outburst, direct intervention in the Syrian conflict could be counter-productive. "Violence breeds violence," he said.

Mr Cameron should reflect on the outcome of the recent war in Iraq, and also on the ongoing war in Afghanistan, where the death toll for our US allies has just reached 2000. He should also understand that millions upon millions of people in the emerging economies of the world think it's "preposterous", to quote Dambisa Moyo, the acclaimed Zambian economist, that Britain should have a place on the Security Council at all.

Thousands of British troops were sent to Iraq; thousands more are still in Afghanistan. What has been achieved, other than a lot of heroic sacrifice? The carnage in Iraq was horrendous, and it is continuing even now, long after the "war" ended. In Afghanistan, Britain is supposed to be helping to eliminate al Qaeda. But al Qaeda is a slippery, fluid foe, and can easily move elsewhere. And when the war in Afghanistan is finally finished, the Chinese will probably move in, peacefully.

Mr Cameron's colleague, Foreign Secretary William Hague, has been vociferous in his support for the recent uprisings in Arab countries, collectively known as the Arab Spring. Well, to paraphrase the Chinese saying, beware of what you wish for. As a direct result of the Arab Spring, al Qaeda is now strengthening its position along the southern Mediterranean littoral, particularly in Libya. With each day, it gets nearer and nearer the heartlands of Europe. It must be defeated, but it will not be defeated by fighting military campaigns in faraway countries which few of our politicians or diplomats seem to understand.

I am not deprecating the Arab Spring, and I am most certainly not defending the repellent regime in Syria. But what is the point of overthrowing one regime, however odious, if you don't know what will replace it? What if it is replaced by a void, a power vacuum? What if it is replaced by a regime that may be little better – and quite possibly more inimical to our own interests?

Mr Putin is right. Violence does breed violence. Mr Cameron should be practising diplomacy. We should be building up our trade with Russia and China, not lecturing them in a patronising spirit of post-imperial hubris. Trade and diplomacy are ultimately more effective than war, which should be a last, desperate resort.

Increasingly I think that the best single reason to support the SNP is that an independent Scotland would have a realistic and responsible foreign policy. Scotland could take a positive if modest role in the world – "Stop the world, we want to get on", as Winnie Ewing once said – instead of posturing in a vainglorious way at the UN, or sending troops to fight futile wars we can never win. An independent Scotland with an export-led economy could be an effective member of international trade bodies, as so many small nations already are.

And I haven't yet mentioned Trident. Tony Blair let the proverbial cat out of the nasty-smelling bag when he wrote that giving up Trident would mean "too big a downgrading of our status as a nation. (he meant the UK, not Scotland, where Trident is based).

I cannot envisage any leader of an independent Scotland clinging to weapons of mass destruction to protect some mythical "status".