Robert Fisk is Middle East correspondent of The Independent.

No entry to the International Red Cross. Not yet. Maybe in a few days, when the area has been secured. Men and boys separated from the women and children. Streams of refugees. Women, children, the old, few males. Stories of men being loaded on to trucks and taken away. Destination unknown. Devastation. No journalists, no freedom of movement for the UN. The place was called Srebrenica.

Parallels are seductive, dangerous, frightening, often inaccurate. Nasser was the "Mussolini of the Nile" to Eden in 1956, Saddam the "Hitler of the Tigris" to Bush and Blair in 2003. Standing up to tyrants – unless they happen to be "our" tyrants – has been quite the thing. It's only when we don't stand up to them that we get a bit queasy and start asking awkward questions. Why did we "stand idly by"? Hafez el-Assad's massacre of his Sunni Islamist opponents at Hama in 1982 comes to mind. Saddam's massacre of his Shia and Kurdish opponents in 1991. Srebrenica, of course. And now Homs. In Libya, as Gaddafi advanced on Benghazi, it was "chocks away!" During Homs, our chaps lingered at dispersal and the "scramble" never sounded.

Yes, the phantoms of Srebrenica move across our planet faster than we realise, high-speed ghosts whose shadows darken the prisons of Libya and then the towns of Syria. Or maybe those ghosts of Hama – Hama of the nouriya water-wheels, still creaking away as the Syrian Defence Brigades battled their way through the city's underground tunnels 30 years ago, fighting Islamist suicide girls with grenades strapped to their bodies – had visited Srebrenica before its fall in 1995. Mass killings, executions are a kind of revolving wheel. Now you see them. Now you don't. And afterwards, we all ask "why?" How did we let it happen?..