I doubt if there are many "monuments men" in Syria just now. George Clooney is not filming on the streets of Damascus. When people are dying in their thousands, it is hard to look at the fate of monuments. But when the horrors of civil war pass, Syria's heritage, the most glorious in the eastern Mediterranean, will have to be rebuilt. War's survivors recover. Their past may not. Syria will one day need the greatest campaign of historical rescue of modern times. We should be ready.

The indiscriminate bombing and shelling of Syrian cities, by whichever side, has devastated ancient Aleppo and the old city at Homs. Crac des Chevaliers, the grandest and best-preserved of crusader castles, has been pummelled by Syrian jets, as has Saladin's fortress at Qal'at Salah el-Din. The 11th-century minaret of Aleppo's Umayyad mosque is now a heap of rubble in the courtyard below. The exquisite Souk al-Madina, hub of the silk route trade since before Christ, is a gutted ruin. Everywhere has been looted.

Syria thus joins Iraq, Afghanistan and Libya in the roll-call of ancient cultures desecrated by modern war, much of it by western bombers. The looting of Iraq's national museum in Baghdad and damaging of Babylon; the demolition of the Bamiyan Buddhas and the obliteration of Libya's Cyrene recall the militarily senseless devastation of the second world war. It disregards the 1954 Hague convention respecting cultural properties during war, which Britain still refuses to ratify in deference to the RAF.

War's destructiveness is a fact of life. War's aftermath is a matter of furious opinion. Should its ruins be left as gruesome memorials to war, should they be restored in defiance of war's obscenity, or should such traces of the past be bulldozed to make way for a new age?

After the second world war, the British cities of Bristol, Plymouth, Coventry and elsewhere swept away more of their old centres than the Blitz ever managed, leaving fragments of churches as witness to Britain's obsession with war. In contrast, Leningrad, Dresden, St Malo and Caen rebuilt their broken cathedrals, palaces and streets, refusing to let war's madness obliterate memory and continuity. The people of Warsaw reconstructed their squares from old photographs. Historicist feuds over authenticity against reproduction were of no concern to them. In 2005 Dresden's baroque masterpiece, the Frauenkirche, was reopened, rebuilt as a tribute from the old Germany to the new. Britain merely left the gutted shell of old Coventry cathedral.

These arguments refuse to vanish. Afghanistan's two giant Bamiyan Buddhas were blown up in 2001 by Taliban iconoclasts in the mountains north of Kabul. They left gaping holes in the mountainside. The Afghan government and the local Hazara people wanted them rebuilt, in defiance of the Taliban, and because the niches look absurd when empty.

The outline of where ancient Buddha statues once stood in Bamiyan. Photograph: Shah Marai/AFP/Getty Images

For a decade, Unesco fanatics – who seem to regard the site as theirs – played medieval schoolmen in arcane disputes on the ethics of Bamiyan. Afghan opinion was of no account. While Unesco's members spent billions of dollars bombing Afghanistan to bits, it treated Bamiyan as might a distant imperial ruler. In 2012 it finally decided the Buddhas should not be re-carved, declaring ludicrously that the site would lose its world heritage status if that happened.

Unesco's scrambled ideology states that a ruin of a ruin is "better" than a ruin. Even though half the world's great monuments are jumbled mixes of restoration and reproduction, it was decided that Bamiyan's gaping holes should stand as a memorial to the Taliban's awfulness, with a "museum of awareness" nearby. The Taliban must have cheered the accolade.

Is this to be Syria's fate? The cult of the ruin holds that the past is something either to be eliminated as useless – the fate of post-civil war Beirut – or to be left untouched, to mature like fine wine in the imagination. The idea that a nation's morale and sense of identity might be sustained by restoring its structures and artefacts is anathema to the cult. The past is for curated ruins and museum professionals.

Poets, artists, novelists and art historians have become the high priests of ruination. The author of In Ruins, Christopher Woodward, records how the relics of "war and violence, poverty and failure, natural disaster and neglect" can be elevated and awarded "if not beauty, then a kind of meaning". A fascinating exhibition currently at Tate Britain even mistranslates the German Ruinenlust (or longing) as "ruin lust", to give ruins erotic force. The ruin is seen as truthful and authentic, but its restoration to useful life or popular meaning as somehow immoral.

The cathedrals of Europe, the palaces of Russia, the temples of Kyoto, the market towns of England, have been rebuilt over and again as peoples treasure their status in community self-consciousness. Their destruction, as by British planners after the war, arises from some Orwellian yearning to deny the past and engineer a new society, usually to make someone money. The irony is that nowadays the old is growing so rare as to hold the key to future profit from tourism.

The greatest debt we can pay to conflict is not to celebrate it, as first world war fetishists are doing in Britain. It is to repair its ravages in honour of the collective memory that war sought to rupture. Unesco can go on with its conferences. The rest of us should stand ready to rebuild, down to the last glorious relic, the marvels of Syria's past, for it is also ours.