The left relies on facts, leaving emotion to the right. But why?

Everyone who cares about how freedom lives, and dies, should visit the Topography of Terror in Berlin. Built in the hulking shadow of Hermann Goering’s air ministry complex and on the site of the wartime Gestapo HQ, this permanent exhibition tells the story of the Third Reich and its crimes.

It does so not through portentous rhetoric but with concrete data, lucid explanations and – above all – panel after panel of unforgettable photographs.

Take the shot of a crowd of workers at the Blohm & Voss shipyard in Hamburg as Adolf Hitler speaks to them in 1936. Your eyes scan the docile legion of Sieg Heil-ing drones – and dupes – with outstretched arms. Then they settle on the solitary figure who stubbornly refuses to salute the Führer. Who was he, and where did he find the courage or understanding to reject the idolatrous herd?

Thanks to his daughter, we know that August Landmesser joined the Nazi party in the early 1930s. But he had a Jewish wife, Irma Eckler. The couple had two children. Whatever their inner doubts, no one else in that almost-unanimous crowd allowed secret scepticism to break cover into visible dissent. Arms proudly folded, August Landmesser did, thinking maybe of the “non-Aryan” partner who had made a nonsense of fascist mumbo-jumbo. Love made a sort of hero out of him. Later, Landmesser went to jail for betraying his “race”. Irma was murdered in the Bernburg Euthanasia Centre in 1942.

During the 12 years of the Third Reich, Hitler’s genocidal regime faced dismayingly few protests on a larger scale than Landmesser’s. Probably the biggest took place on Rosenstrasse in Berlin in 1943. Hundreds of “Aryan” women gathered to march against a decree that had extended deportation orders to their Jewish husbands and other relatives. Repeatedly, they defied armed SS men outside the detention centre to demand the release of family members. Remarkably, the protest worked and the order was rescinded. Auschwitz and other camps claimed a couple of thousand fewer victims.

Of course, millions of Germans ought to have cried out in shame and horror on every single day of Hitler’s rule. They did not. But the bonds of affection, loyalty and kinship could prevail even against the Gestapo’s reign of terror. It took private needs and longings to make the call for justice heard on the streets of tyranny.

Rational calculus alone will seldom push people to withstand social or political evil, or to struggle for equality and reform. Justice needs passion as much as hatred does. Now turn to the US today, and its increasingly bizarre presidential race. On Tuesday, Donald Trump won primary contests from Illinois to Florida. He has triumphed in 18 out of 27 states and stands within hailing distance of the 1,237 delegates required to secure the Republican nomination. This week, a forecasting firm rated his chances of getting them at 78 per cent.

Trump is no Hitler. On his long-term record, he does not even count as a committed right-wing ideologist. As ultra-conservative career head-bangers, Ted Cruz and Marco Rubio – on whose electoral corpses he stomps – outrank The Donald by a league. One of the cuter conspiracy theories in this year of topsy-turvy politics maintains that Trump entered the race as a payback favour to his chum Bill Clinton in order to guarantee the election of Hillary.

Whatever his mixed and murky motives, Trump has jumped ahead because he gives voice to pure, unbridled passion, oblivious to reason and unshackled by facts. The shameless demagogue has harnessed to his chariot of cant the four horsemen of the post-slump apocalypse: anger, fear, resentment and grievance.

The violence that now breaks out at Trump rallies whenever a heckler interrupts looks like the spume atop a deep whirlpool of fury and suspicion. Forget those routine departures from reality that lead Trump partisans to believe that Barack Obama is a foreign-born Muslim, or that the British NHS runs “death panels” for ailing pensioners. For the grudge-driven voter, wrathful paranoia can prove a – literally – fatal disease.

During the US flu pandemic of 2009-10, shock-jock radio hosts such as Rush Limbaugh attacked federally funded protective jabs as socialistic meddling by the Islamo-Bolshevik Obama. As a result, Democrats proved much more willing to seek the injections than Republicans. It seems that many extreme conservatives are willing to die for their prejudices.

Ever since rabble-rousing demagoguery began to tweak the new democracy of the late 19th century, rational progressives have feared the hysterical crowd. They championed the “people” but not the mob-like “mass”. In the 1890s France of the Dreyfus affair, with Jews and migrants the target of mob frenzy, Gustave Le Bon wrote in The Crowd about the “anonymity, contagion and suggestibility” that, en masse, reduced a thinking being to “a grain of sand amid other grains of sand”. This barbarian herd needed to follow a cultic leader. “It is terrible,” warned Le Bon, “to think of the power that strong conviction combined with extreme narrowness of mind gives a man possessing prestige.”

Remind you of anyone? In 1922, Sigmund Freud built on Le Bon’s work for his essay on group psychology and ego analysis. To Freud, writing in the wake of the xenophobic hurricanes of the First World War, the modern mass-hysterical crowd is not so much a herd as a horde: a revival of the “primal horde” led by a “primal father”, “absolutely narcissistic, but self-confident and independent”. Freud says nothing about hair replacement as an attribute of primitive charisma. He does insist that members of the demagogue-directed crowd become disinhibited children again. They exhibit a “picture of regression of mental activity to an earlier stage”. A decade after Freud wrote, Hitler came to power.

With the best of motives, the non-violent and non-Leninist left has always feared this “primal horde”. True, a Sanders or a Corbyn can enlist righteous indignation against yawning inequality and the diminution of life-chances for the poor, the young and the non-white. Yet that urge for equity adopts polite, reasonable and evidence-based forms. Mainstream progressive movements long ago forsook class hatred for intellectual persuasion. In the 1880s, the Fabian Society set up shop as a “fact-finding and fact-dispensing body”: the first of many to climb towards the New Jerusalem on a staircase carpentered from reason alone. Later, as affluence spread and the truly deprived became “them” rather than “us”, democratic socialists no longer denounced their foes as (in Nye Bevan’s Trump-like term for the Tories) “lower than vermin”.

Even after the meltdown of 2008, when the monumental irresponsibility of a feather-bedded few really did deserve rancour and contempt, banker-bashing failed to gain much traction. Fred Goodwin and his chums never came within striking distance of a handcuff – or a fisticuff. Instead, fashionable warriors for social justice began to brandish sweetly reasonable manifestos such as Kate Pickett and Richard Wilkinson’s much-admired study The Spirit Level. This sensible and scholarly defence of lower income differentials as the precondition of a happier society changed minds but would hardly man a barricade. On the rationalistic left, treatises and statistics, not catcalls and cobblestones, have for a century made the case for betterment.

The politics of witness and experience has not quite fled progressive ranks. From the civil-rights movement of the 1960s to the Black Lives Matter movement now, it survives in heartfelt action for equality. A hunger for racial justice may even top the polls. In county elections in Ohio and Illinois this week, challenger candidates backed by Black Lives Matter ousted incumbent prosecutors who had allegedly failed to take swift action on fatal shootings by police. A passion for dignity swayed those local votes, and swayed them left.

Still, these brushfires at the margins seldom scorch the middle ground. There, every reformist bid for power means the scrupulous elimination of populist toxins. That works well enough when your opponents play by the same rules. Obama’s election in 2008 owed much to the decency of John McCain. Once a Trump turns up, it leaves level-headed improvers with a glaring deficit.

Liberals will never out-scream Trump: that Freudian id on a stick. But they might try – as early-phase Obama did – to channel hope as well as their enemies channel fear. The left’s defective language of emotion has long worried the American cognitive scientist George Lakoff. In books such as Moral Politics, he has exposed the frailty of liberal reason against reactionary fervour and argued for a frankly subjective politics of values and convictions on the left. Lakoff deals in the metaphors we live by, and urges reformers to promote their benign model of the “nurturing family” against the punitive patriarchy of a Trump.

Here, Old Labour once commanded that feelgood language of sharing and community. New Labour dumped it as an outdated relic. Corbyn Labour can speak warmly to itself but not, so far, to the wider national family. Somehow, the side of the angels needs to argue for tolerance, compassion and solidarity as human impulses just as profound, indeed visceral, as the drives to destruction recruited by the demagogic right. They might start with a glance at August Landmesser, whose family values kept his arms folded while the world went mad around him.