At least the west is agreed on the Ukraine crisis. It agrees that something must be done to stop Russia's re-occupation of Crimea, and it agrees that nothing can be done to stop it. Paradox is the stuff of foreign policy. It produces summits, holds conferences, forms and reforms contact groups. Leaders make interminable phone calls and thinktanks rush joyfully to club-class lounges. Everywhere, something must be done and nothing can be done. Must fights can.

On Monday night I visited a Ukraine seminar in Westminster organised by Prospect magazine. It was crammed with diplomats, defence experts and Russian and Ukrainian pundits, and was a sombre occasion. The understand-Russia tribe argued with the understand-Ukraine tribe. Legal sticklers fought pragmatists. Stand-firmers fought realpolitikers. Putin's bombast was pitted against Putin's paranoia. The west's righteous indignation was pitted against its double standards.

Yet all agreed on one thing. Something must be done. It was not a seminar on Ukraine, it was a meeting of the global trade union of professional something-must-be-dones. Participants were curiously liberated by the impossibility of driving Vladimir Putin out of Crimea by force. Since military hawks have had to take leave of absence from this crisis, diplomatic ones were having a field day. The masters of the velvet glove seemed not to mind they had no iron fist inside it.

Hence we enjoyed the familiar cold buffet of messages, warnings, deterrents, red lines, sanctions, gestures, carrots and sticks. To the do-something persuasion appearance is crucial, because appearances are cheap. Thus Barack Obama "must not appear weak", Nato must give "a clear signal", the EU must appear united. The air is thick with unacceptables, inexcusables and intolerables. Gestures are stock in trade. The US secretary of state, John Kerry, must decline to meet his Russian counterpart. Lots of people must refuse to attend Olympics and conferences – a sanction of peculiar savagery to any do-something.

I am no Kremlinologist, but I find the idea that such gestures might leave Putin quaking in his boots as ludicrous as the idea that they terrified Osama bin Laden or the Taliban. Great emphasis is laid on making Putin and "those round him" realise they have "miscalculated" the west's response. Yet every one of these gestures seems utterly predictable. Bombs and drones may break your bones but, when these thugs go to war, words will never hurt you. At which point, "something" escalates into our old friend, economic sanctions. As David Cameron and Obama say over and again, "Putin must know that there is a price to pay for his actions." Some think visas should be withdrawn with blood-curdling screams: "Your oligarchs will never darken the doors of Harvey Nicks again!" Others think sanctions should be quietly imposed through border controls on "bad guys". It is a strange world that equates invading Crimea with being banned from Kensington.

Then come the celebrated "options" – the nuclear sanction of freezing bank balances, stopping credit lines, cancelling barter deals and suspending joint projects. An upward ratchet of supposed misery is to be imposed on Russians, somehow commensurate with Putin's increasing lawlessness. It is the diplomats' equivalent of "bombing the enemy back to the stone age". This will teach them, they cry. This will deter them.

The rationale is puzzling. It has always been doubtful that the maxim "It's the economy, stupid" applies to international relations, especially those involving the economies of authoritarian regimes. Putin will have embarked on his Crimean adventure with some assessment of possible retaliation and, if not, with an acceptance that the retaliation was worth it. Pushing back at Nato and the EU after two decades of sustained advance along Russia's eastern border has been hugely popular. National pride usually trumps cost.

Besides, Russia is now a serious economic player, if not on the scale of China. It is not Iraq or Afghanistan or Burma, small poor countries that western governments can easily impoverish to suit their moral whims. Russia can at least reply with a degree of mayhem, as indicated in last week's leaked (and sensible) Downing Street memorandum. Germany, increasingly a point of sanity in European diplomacy, clearly opposes cutting relations with Russia over Crimea. Trade is in all of Europe's interest, and is the long-term glue most likely to reduce friction between Europe and Russia.

I accept that there are conversations between states that sometimes require plain speaking. But the words must be fit for the purpose in hand. This would surely extend to an acceptance of what used to be called "spheres of interest" along the still new and sensitive borders in Europe and Asia. Putin's rectifying of Nikita Khrushchev's 1954 "donation" of Crimea to Ukraine may be technically illegal. So was the west's war on Serbia over Kosovo. It is hardly on a par with Hitler's invasion of the Sudetenland, or the west's violent seizure of Iraq and Afghanistan. In the catalogue of global outrage, it is no big deal.

In his book America and the Imperialism of Ignorance, Andrew Alexander showed from an examination of Soviet documents how far the west misjudged Moscow's intentions during the cold war. A mix of belligerent posturing and over-reaction to provocation was heavily driven by the Pentagon's military-industrial complex, with Nato trotting along behind. The result took an appalling risk with European security, and at a horrific cost.

The current response to Crimea shows how easily misjudgment can emerge from such political machismo. Perhaps the better parallel is Sarajevo 1914. One leader's wounded pride triggers another's pursuit of self-interest, a reckless treaty triggers a pre-emptive strike. Bluffs are called, prices thought "worth paying". As pandemonium ensues, no one can recall how it all started.

Today's reign of the do-somethings is oozing from the musty corridors of a once-imperial Foreign Office. It is seeping from under-employed defence lobbyists and thinktanks. It begs, weeps, screams that "something must be done" about Crimea. It derides "doing nothing" as so much wimpish, pseudo-pacifist appeasement. It must, or how else will Chatham House feed its young?

Russia's occupation of Crimea may or may not reflect Putin's paranoia at the west's muscle-flexing along its border. Kiev's fight for independence may or may not reflect a justified fear of Russian revanchism. I do not know. I know only that neither country threatens us, and neither "belongs to us". Some people just cannot bear to be left out of a fight.