I don’t know if you’ve ever picked up the phone and found Sir Nicholas Soames on the other end, but I’d recommend it. Even if the formerly portly Tory MP is rankled, a couple of minutes’ chat still acts as a quick dip into a Pall Mall port party around 1952. Bracing, clubby, slightly intoxicating.

This happened to me earlier this week, when I was reporting on how the shoot for the fifth Transformers movie had commandeered Blenheim Palace and turned Churchill’s birthplace into Hitler’s headquarters. There were stormtroopers in the forecourt, swastikas down the walls – and a front-page headline in the Sun: “Goose-stepping on Churchill’s grave”.

The story quoted outraged military types who said Churchill would be spinning six feet under. The film’s director, Michael Bay, counterattacked by saying that actually he’d be smiling, as Transformers 5 shows him to be noble. Hence Soames returning my call: who better to have the inside track than his own grandson?

But Soames said he had no idea what Churchill’s reaction would be, and no one could. The whole hoo-ha was, he felt, dismal, idiotic, absurd and pathetic. The Sun had simply sought out “some wretched veteran who is prepared to say, ‘Winston would be turning into his grave.’ They’ve no idea what my grandfather would have thought! It’s preposterous. Why can’t they make a film at Blenheim 75 years after?”

Naturally, this is true. One might speculate for ever about the feelings of a man born in 1874 about production design on a film featuring robots disguised as trucks. Perhaps he’d have cheered the coffers coming in from Paramount. Given his eye for theatrics, he might have applauded Bay for expanding the range of locations used in cinema. Or he might have been amazed that the Nazis remain such touchpaper. Blenheim was built to reward the first Duke of Marlborough for his triumph over the French; if a movie recast the palace as Napoleon’s HQ (had he invaded Britain), the film-makers’ audacity would likely go less checked.

But for me the crucial date is the half-century since Churchill’s funeral. What is the cutoff for confidently laying claim to knowing what the dead would have said? It’s probably safe to say, for instance, that John F Kennedy wouldn’t have minded Lyndon B Johnson invoking his name to help push through the civil rights act the year after Kennedy’s assassination. But what about decades later? Can even JFK’s closest surviving advisers be trusted to know what he would have thought about Donald Trump?

Guessing the verdicts of dead heroes isn’t a new pastime, of course – religions have long split over the interpretation of the instructions of deceased leaders – and nor is merrily disregarding the explicit wishes of the deceased. The specially built gallery that was a condition of JMW Turner leaving his paintings to the nation never materialised. Philip Larkin didn’t want to be seen dead in Westminster Abbey’s Poets’ Corner, but still wound up there. Likewise Thomas Hardy, though his widow compromised by deciding to have his heart buried in the local churchyard and inter his ashes in the abbey. (Unfortunately the doctor who removed Hardy’s heart briefly left the room soon after and, when he came back, found a cat eating it. The moggy was therefore killed and buried alongside what was left of the heart.)

But lately such morbid speculation seems to have stepped up a gear. In the Conservative party, what Margaret Thatcher might have thought about almost anything is considered a killer argument for or against it. Churchill himself was appropriated by both sides of the Brexit debate. And I think this stems from a very modern sense that we ought to have opinions about everything, all the time – fuelled, of course, by social media. Having expired is no excuse for not having a view.

Comment is paramount; facts are relegated. This is why Trump still gets away with spouting rubbish despite all of us being ably equipped as fact-checkers. The living disregard research, leap upon bandwagons and have little compunction about dusting down corpses to help our cause. We get drunk on the opportunity to spout on a platform, and then feel underwhelmed, even disgruntled, when democracy prioritises the dreams of other people.

One thing that we can be certain Churchill was certain of – because he said it in a speech that was written down – was that being certain is over-rated. “To improve,” he said, “is to change, so to be perfect is to change often.” Holding hard and fast opinions about everything isn’t just impossible if they are to have integrity; it is also boring. The idea that the dead would also do so is doubly odd; we would miss people less if they were always completely predictable.

Being free to change your mind, or free not to voice an opinion, is a liberty that we should embrace more. It is also a privilege that we ought to extend to the dead.