Churchill, hero or villain? Prince Charles, goodie or baddie? Jesus Christ, yes or no? John McDonnell, modern Herodotus or fool? Tick the boxes and pass the GCSE. Welcome to the new history. McDonnell, the shadow chancellor, is entitled to dislike Winston Churchill, but why for Tonypandy? Churchill happened to be Liberal home secretary in 1910 and was asked to authorise a small company of soldiers to help local police during the Rhondda disturbances. He did so with reluctance and later professed sympathy for the miners. The one man who later died was hit on the head by a Glamorganshire policeman. The soldiers were not involved.

What is this really about? The answer is yah-boo history: binary storytelling charged with fake emotion, sucked dry of fact or balance. It is history as partisan docudrama. Why did McDonnell not mention Churchill’s role in the death of hundreds of thousands of innocent Germans? Does he not care about dead Germans? Is he for bombing civilians?

This may seem harmless fun, like Horrible Histories and 1066 and All That, or like “faction” films such as Vice and The Favourite. But we can disregard comedians and film-makers. We cannot disregard serious politicians. McDonnell may have been caught off guard, but this is not harmless. As history is raided, indeed raped, by identitarians and populists, glib judgments on the past become fodder for every tribal grievance. In Wales, any myth is history if the English are involved – though on Tonypandy I commend BBC Wales’s history blog by Phil Carradice.

Reassessing Churchill has moved from cottage industry to parlour game. His career straddled the most turbulent period in modern times, the strain of which on public figures should make current politicians hold their tongues. Churchill was elected a Tory in 1900 but soon switched to the Liberal party, where as home secretary he supported prison reform and Lloyd George’s early moves on social security. In the first world war he resigned after the catastrophic Gallipoli campaign, which he had conceived as navy minister. He then rejoined the Tories, declaring, “Anyone can rat … it takes ingenuity to re-rat.”

Churchill was not a good minister. He was at the exchequer from 1925 to 1929, presiding over the general strike and the return to the gold standard, partial cause of the Great Depression. Such was his unpopularity on all sides that he stayed on the backbenches throughout the 1930s. The second world war was his godsend, as his warnings about Hitler made him the one Tory acceptable to the Labour opposition as wartime coalition leader.

Roy Jenkins regarded Churchill as outranking even Gladstone among great Britons, but that was on his war record, a topic again subject to revision. A capacity to rally people to a common purpose, to support them with rhetoric and vigour and to lead them to victory, is a mark of greatness. But victory in 1945 was thanks to the Americans and Russians, not to Churchill. Other than in north Africa, he was chiefly preoccupied with securing American aid, and with the costly and pointless flattening of German cities. As Lord Alanbrooke’s diaries indicate, Churchill had constantly to be restrained from poor decisions by those around him. As for being applauded for victory, the electorate turfed him out before the war was even over. He then remarked that “history will be kind to me because I intend to write it”, which he did with panache. Churchill was a remarkable war leader, but he was a better writer than politician.

The idea of history as composed of heroes and villains is infantile. Inside every hero lurks an opposite. The best answer to a stupid question is no answer, as McDonnell said when asked his favourite Tory. Fake history may be a clever way to engage the empathy of the young with otherwise difficult material. But if the purpose of history is to offer lessons for the future, distorting it is fraught with danger.

The current cult of identity politics is to rifle through the past careers of great men and women, not to ascertain accuracy but to sort them into friends or foes. Churchill has been accused of racism. He undoubtedly expressed racist views but they were uttered in very different times, in which such ideas were deemed acceptable by many.

Gladstone as a young MP lobbied for the slave owners, who included his father. He did not support slavery, as is often said, merely the compensation of owners forced to abandon it. He did not extend that charity to the slaves, but I do not see how this impinges on his accomplishments – greater, surely, than Churchill’s – to such an extent that his name must be shielded from delicate eyes at Liverpool University.

History is a vast and subtle canvas. I have come away from working on a history of Europe convinced that it is senseless to pass moral judgment on men and women of past times and past cultures. Awarding long-dead people berths in some transient heaven or hell is merely to conscript them to some current grievance. The relentless rewriting of old feuds – Scotland’s Flodden Field, Cromwell’s Drogheda, Rhondda’s riots – still lies at the root of so many of Britain’s domestic woes.

I am convinced a historic British aversion to the Germans, rehearsed annually on Remembrance Day and in movies and bestseller lists, underpins much current Brexit sentiment. So does ancient antagonism towards the French. Fake history is worse than no history. It is better to forget than partially to remember. We should live for today and move on.

• Simon Jenkins is a Guardian columnist