Robert Fisk: Could there be some bad guys among the rebels too?

John McCain backed the good guys in Libya, who are now keenly torturing their opponents to death.

The same John McCain now backs the good guys in Syria – no "boots on the ground", mind you, for this is war without death for America – and it all seems OK, until I sit opposite a guy over coffee in Beirut who kind of makes the whole story a bit more complicated. We back surrounded minorities, fighting bravely for their rights against overwhelming odds – Homs, for example. We did the same when the Kosovo Liberation Army – not exactly the squeaky-clean outfit that Nato would have us believe until Slobodan Milosevic surrendered – fought against overwhelming Serbian odds in 1998.

Maybe it goes back to the Paris Commune of 1871 – French versus French, but let's forget that bit – or the Warsaw Uprising, or the 1944 Liberation of Paris. The French used to talk about les tireurs des toits – the roof marksmen – who assaulted even Charles de Gaulle when he entered Notre Dame on the day of liberation. Homs, of course, has its own tireurs des toits: Syrian government snipers on the roofs – Iranians according to the Syrian opposition. As if the Syrian military needs to be taught how to shoot by the slightly decrepit Revolutionary Guards of Tehran. Stories of the brutality and cruelty of Syrian officials are true. Let's repeat that: stories, reports, images, YouTube, real recordings of these cruelties, are all true. But then there's the shocked face of my friend, neither Syrian nor a journalist, drinking coffee with me, who agrees with much of the story. Snipers, yes. "Most of the shooting victims are hit in the head or chest. If you are hit by a sniper, you are in a serious way." There has been shelling – of homes and of at least one clinic – and there are graves in gardens. But then there are the other little comments, almost forgettable but still disturbing. The habit of "Free Syrian Army" soldiers of playing Islamic music before crossing roads under sniper fire and of praying before pressing their foot on the gas. Well, nothing wrong in that, for heaven's sake.

Then the large number of FSA men who appear to be Islamist rather than Islamic – this subtle difference is initially hard to spot, says my friend. And then the boasts of "armed activists" in Homs – there now seems to be a gentle difference between activists (armed) and protesters (unarmed) – who are executing their Alawite and Christian neighbours.

Could it be that the brave defenders of Homs include some very bad guys? Well, you may say, who can blame them? What resistance force, defending its people, has not admitted that "there may have been some excesses"?

My friend (no acolyte of the Baath party) expresses his absolute belief that if the FSA breaks out of Homs, there will be "massacres". The ethnic cleansing of the Christians, then, the nightmare that Assad evokes? And the rumours that Syrian tanks use heavy machine guns in cities but growl around without shells for their barrels – just in case they, too, defect? Could it be that shelling Homs is one thing, but levelling it to the ground a much more painful gamble of "will the tank-crews defect or not"?