I didn’t sleep much on Monday night. I spent it trawling social media, glued to accounts I’ve followed since I first started writing about the Syria crisis four years ago. In our hyper-connected world, as Twitter floods with gruesome images from Aleppo, the gore is almost close enough to smell.

These aren’t random sources of propaganda. They are activists in situ whose accounts been consistently corroborated by external monitors when reporting atrocities. Some are friends or relatives of refugees I work with in Europe; people I know and trust.

On Monday, they were awaiting death and – here’s a 21st-century phrase – tweeting out their final farewells.

When regime forces seized the Al-Hayat hospital on Monday, executing its entire medical staff on sight, it surprised nobody familiar with Bashar al-Assad’s repertoire of violence. Reports of women burned alive, a Unicef plea for the 100 children trapped in a besieged building – these were not news stories. It was just another expression of the Assadist-Putinist war machine.

But it is not Shia-nationalist bloodlust that has made my stomach churn this week. Nor is it – though it comes close – the rolling drum beat of denialists, those twitter bots who question each claim of bloodshed or who eject, like a well-timed toaster, an hourly series of manufactured photographs, supposedly showing regime soldiers performing heroic deeds.

Aleppo before the Syrian Civil War Show all 12 1 /12 Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man crosses a street in Aleppo, December 12, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A vendor sits inside an antique shop in al-Jdeideh neighbourhood, in the Old City of Aleppo, December 12, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A view shows part of Aleppo's historic citadel, overlooking Aleppo city, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A view shows part of Aleppo's historic citadel, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Visitors walk inside Aleppo's Umayyad mosque, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk inside the Khan al-Shounah market, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man walks past shops in al-Jdeideh neighbourhood, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk along an alley in al-Jdeideh neighbourhood, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Visitors tour Aleppo's historic citadel, Syria December 11, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A general view shows the Old City of Aleppo as seen from Aleppo's historic citadel, Syria December 11, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk near Aleppo's Bab al-Faraj Clock Tower, Syria October 6, 2010 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man stands inside Aleppo's historic citadel, overlooking Aleppo city, Syria December 11, 2009 Reuters

Late on Monday, I spotted an acquaintance electronically wringing her hands. “Why has nothing been done?” she tweeted. “Why has our Government not helped?”

British interventions in Middle Eastern countries have a long, shameful history, strewn with error and bad faith. Nevertheless, the government bill proposed by David Cameron in August 2013 represented our best chance of maintaining safe corridors of aid to civilians and evacuating besieged cities. It is unlikely to have ensured a long-term peace in Syria, but it would have demonstrated to President Assad – and President Putin – that atrocities against civilians would earn a military response; that we were serious in our peacekeeping commitments.

It was as measured and democratic as any proposal on UK intervention could have been, attempting a consensus in parliament despite the longstanding principle that the Queen and her ministers can authorise military force without it.

Here are the crucial words of that bill (they follow a discussion of the UN report into the US of chemical weapons by Damascus): “[This House] believes that the United Nations Security Council must have the opportunity immediately to consider that briefing and that every effort should be made to secure a Security Council Resolution backing military action before any such action is taken, and notes that before any direct British involvement in such action a further vote of the House of Commons will take place; and notes that this Resolution relates solely to efforts to alleviate humanitarian suffering by deterring use of chemical weapons and does not sanction any action in Syria with wider objectives.”

Dry reading – but consider the extraordinarily accommodating nature of this deal. Imagine any other bill in which a prime minister committed himself to returning to the house for a second vote before enacting its provisions. Those who voted against it did not only vote against the possibility of a military response to Assad’s use of chemical weapons, they voted against the subject ever being raised again in parliament.

Those who now claim they could have accepted another compromise from David Cameron should explain why they so jovially cheered his Commons defeat. This was not a considered response to genocide, it was a political game to undermine the Prime Minister.

If you are tweeting angrily, today, about our Government “failing to do something”, ask yourself carefully what doing something looks like. If you believe Aleppo could have been helped ere now by the British Government – and by the UN consensus David Cameron so earnestly sought in 2013 – you must accept two things. The first is that President Assad is not our ally; that he has committed crimes against humanity every bit as heinous as Isis (which he helped cultivate.) The second is that to make any difference, even if only to man a few planes, British men and women would have had to don uniform and head for a foreign territory.

Syria conflict: Aleppo civilians post 'goodbye' videos

Theresa May, for all her usual neutrality on Tory splits, co-sponsored David Cameron’s bill in 2013. If you believe our Conservative prime ministers have ignored the issue, have somehow colluded in this misery, shame on you. If you believe that we could have eased our consciences, avoided this week’s uncomfortable headlines and not risked British lives, shame on you.

Others have written before – and written well – on the deceit and self-interest which marked Ed Miliband’s management of Labour’s response in 2013. Jeremy Corbyn, Caroline Lucas, Paul Flynn, Elfin Llwyd, Jonathan Edwards and Hywel Williams all played a hand in the wrecking amendment to the bill that was the first step in its death, whose pressure on Miliband led to his duplicity, who repeatedly poured doubt on the claim that Assad was behind chemical attacks in 2013. This year, Lucas has begun seriously criticising both Russia and Syria’s record of human rights. Perhaps the images from Aleppo this week might convince the others that President Assad isn’t so great, too.

These are not the only people responsible for Britain’s colossal failure in the face of genocide. David Davis, a man fond of abstract principles, and who now sits gleefully on the Tory front bench as Minister for Brexit, led the government rebellion against intervention in 2013. In 2005, he lost a Conservative leadership election campaign to David Cameron; his bitter resentment – refusing every olive branch, every possibility of a return to the cabinet table – is the stuff of Commons legend.

And David Cameron himself mismanaged the 2013 vote, summoning back MPs too early from their holidays for two days of panicked negotiations, alienating potential friends.

More culpable are the journalists you can find on the pages of every newspaper who have repeated Assadist propaganda. You can spot them by their readiness to identify Isis as combatants in Aleppo, to dismiss reports of civilian deaths in the city. Ask them why the regime has focused its attention this week on Aleppo, so full of civilians, instead of preventing Isis from retaking Palmyra? If they mumble something about Isis’ advance on Palmyra being funded by America, they’re either nuts or complicit.

If you have willingly consumed such propaganda, then you too play a part in our guilt this week. If you have told a polling company you’ll never vote for an MP who authorises the firing of a single shot, if you have muttered “never again” in school assemblies but called endlessly for more evidence of Assad’s proven atrocities, if you have tweeted prayers but baulked at action, then you are to blame.