Every day, a new massacre is reported in Syria. Yesterday, it was Daraya. Slaughter by Syrian troops, according to those opposed to Bashar al-Assad. Slaughter by Bashar's "terrorist" opponents, the Syrian army said, producing the wife of a soldier whom they said had been shot and left for dead in a Daraya graveyard.

Of course, all armies want to stay clean. All that gold braid, all those battle honours, all that parade-ground semper fi. Thank God for Our Boys. Trouble is that when they go to war, armies ally themselves to the most unsavoury militias, gunmen, reservists, killers and mass murderers, often local vigilante groups who invariably contaminate the men in smart uniforms and high falutin' traditions, until the generals and colonels have to re-invent themselves and their history.

Take the Syrian army. It kills civilians but claims to take every care to avoid "collateral damage". The Israelis say the same. The Brits say the same, the Americans and French. And of course, when an insurgent group – the Free Syrian Army or Salafists – set up positions in the cities and towns of Syria, government forces open fire on them, kill civilians, thousands of refugees cross the border and CNN reports – as it did on Friday night – that refugees cursed Bashar al-Assad as they fled their homes.

And I cannot forget how Al Jazeera, loathed by Bashar now as it was once hated by Saddam, came back from Basra in 2003 with terrifying footage of dead and wounded Iraqi women and children who had been shredded by British artillery firing at the Iraqi army. And we don't need to mention all those Afghan wedding parties and innocent tribal villages pulverised by US gunfire and jets and drones.

The Syrian military, whether it admits it or not – and I'm not happy with the replies I got from Syrian officers on the subject last week – work with the shabiha (or "village defenders" as one soldier called them), who are a murderous, largely Alawite rabble who have slaughtered hundreds of Sunni civilians. Maybe the International Court in the Hague will one day name Syrian soldiers responsible for such crimes – be sure they won't touch the West's warriors – but it will be impossible for the Syrian army to write the shabiha out of the history of their war against the "terrorists", "armed groups", Free Syria Army and al-Qa'ida.

The attempted disconnect has already begun. Syrian troops are fighting at the request of their people to defend their country. The shabiha have nothing to do with them. And I have to say – and no, yet again, I am not comparing Bashar with Hitler or the Syrian conflict with the Second World War – that the German Wehrmacht tried to play the same narrative game in 1944 and 1945 and, then, in a much bigger way, in post-war Europe. The disciplined lads of the Wehrmacht never indulged in war crimes or genocide against the Jews in Russia, Ukraine or the Baltic states or Poland or Yugoslavia. No, it was those damned SS criminals or the Einsatzgruppen or the Ukrainian militia or the Lithuanian paramilitary police or the proto-Nazi Ustashe who besmirched the good name of Germany. Bulls***, of course, though German historians who set out to prove the criminality of the Wehrmacht still face abuse.

The Vichy French army tried to clean its claws by claiming that all atrocities were committed by the "Milice", while the Italians blamed it all on the Germans. The Americans used the vilest criminal gangs in Vietnam, the French used colonial troops to massacre insurgents in Algeria. The Brits tolerated the B Specials in Northern Ireland until they invented the Ulster Defence Regiment (UDR), which got contaminated by sectarian killings and was disbanded. No, the UDR was squeaky clean compared to the Germans. But at the height of their Iraqi occupation war, the Americans were paying Sunni "neighbourhood guards" to liquidate their Shia enemies, and paying thug-like reservists – along with quite a few professionals – to torture their prisoners in Abu Ghraib. And then there is Israel – forced to grovel when their own Lebanese Phalangist militia slaughtered 1,700 Palestinians in 1982. Their equally vicious South Lebanon Army militia tortured prisoners with electricity in the Khiam prison inside Israel's occupied zone in southern Lebanon.

Of course, war stains all who take part in it. Wellington's men in the Peninsula Wars could no more prevent their Spanish guerrilla allies committing atrocities than the Brits and Americans could prevent their Soviet allies raping five million German women in 1945. Didn't the Turkish army use its own version of the SS – along with Kurdish militia – to help in the genocide of the Armenians in 1915?

The Allies of the Second World War did their share of extrajudicial executions – though on nothing like the scale of their enemies – and, thanks to YouTube, our very own beloved Free Syria Army has actually advertised its own murders in Syria. Chucking policemen off roofs and shooting shabiha to death after torturing them doesn't burnish the reputations of La Clinton or the messieurs Fabius and Hague. Keeping clean is a dirty business.