IT seems slightly odd that something apparently almost indefensible on logical, political or practical grounds should be extraordinarily, widely and enduringly popular. But it’s surprisingly often the case.

One way to account for it is to reach the unpopular and unspeakable, but obviously true, conclusion that many, or even the majority of, people are often idiots. This has the advantage that you can continue to think of the thing in question – religion, national pride, excessive sentimentality about animals, capitalism, communism, racism, admiring the music of Andrew Lloyd Webber, to take a few examples – as self-evidently wrong, and bemoan the wrong-headedness of the public.

A variant, to disguise the condescension implicit in that approach, is to blame some external factor – class, poor education, capitalism, false consciousness, the mass media, the patriarchy – for people’s failure to see the obvious.

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The more difficult way to think about it is connected, but more rigorous. It is to wonder whether there’s anything to be said for the belief or institution in question – not as an excuse, but rather as a possibly valid objection to your dismissal of it.

For a few – racism, say, or Lloyd Webber – there obviously isn’t, and you can safely mark them down as the products of stupidity or malicious manipulation. But for many others, the conclusion that you would have to reach most often is that these things appeal to some deep-seated instinct or need, and that their value lies in a transcendent quality. Someone who dismisses mythology, for example, because it is not factually accurate or historically verifiable is missing the point: it’s not supposed to be literally true, but to convey some deep, underlying truth.

Monarchy is, on the face of it, a preposterous idea. Apart from anarchists, always a very small minority, most people accept the idea of authority and leadership figures; indeed, it’s a distressing aspect of human psychology that they often actively like them, even when they are repressive and wicked. There are people still prepared to defend Stalin, for example.

Even if you want someone in charge, though, and whether, like dictators, they have absolute power, or like constitutional monarchs or purely figurehead presidents, no real power to speak of, you wouldn’t, if acting strictly rationally, select them on the basis that they all came from the same family. Yet that’s the defining feature of monarchy.

But maybe that’s not as odd as it looks. We apply hereditary principles in most areas of life; the desire to pass things on – money, but other things too – to your children and grandchildren is well embedded in human psychology, even in those who approve of punitive inheritance taxes in theory. Some of the reputation that everyone has is inherited from their parents, at least amongst those who knew them.

The practical argument for a monarchy – rather than, say, a presidency – is fairly straightforward. Monarchs can be unifying and neutral in a way that elected officials very seldom are, and it probably costs about the same to run either system. And, however silly some people find it, the romance and pageantry of royalty is deeply appealing to lots of people, and generates tons of money. Harry and Meghan, while professing to renounce royal status, are clearly relying on it to bring in the dollars; Netflix wouldn’t have forked out as much for a sequel to The Dater’s Handbook.

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With the system of monarchy, however, there’s still the problem that you get whoever’s next in line: it’s the ultimate Buggin’s turn. Sometimes, as with the current Queen, you couldn’t get much luckier. It’s almost impossible to find anyone – however foam-flecked a republican they are – who would argue that she hasn’t done a very good job. The only point where she seemed to stumble was in the immediate aftermath of the death of Diana, Princess of Wales, and some of us still think she was right then, and the Great British Public, not for the first time, had gone collectively bonkers.

Just as often, though, probably more often, you get saddled with someone who’s mediocre or actively bad. You don’t have to go back to Macbeth, King John, Richard III, or homicidal maniacs like Henry VIII. We’ve had the longest reign from one of our best-ever monarchs, but the Queen’s uncle, Edward VIII, with the shortest reign of any UK monarch, was a comprehensive disaster, except as a natty dresser. Not because of Wallis Simpson, the proximate cause of his abdication, but because he was, among numerous other failings, vain, shallow and far too keen on Hitler.

After 70 years, and the death of the Duke of Edinburgh, it’s natural that people should speculate about the future of the monarchy. Whatever his qualities, I think it’s reasonable to claim that, at least at the moment, the Prince of Wales is far less popular than either his mother or his elder son. You occasionally hear folk – usually diehard admirers of the monarchy, actually – say they’d like Prince William to succeed the Queen, skipping him altogether.

That’s rather to miss the basis of the hereditary principle (though there are plenty of precedents for shoving the main candidate aside in favour of someone you prefer the look of). And it’s possible that it could change when Charles ascends the throne; he might easily have a couple of decades in the role and – who knows? – become wildly popular.

But what if it had been his younger brother who was being lined up? The trouble with maintaining an irrational system such as the monarchy is that it depends almost entirely on the qualities of the incumbent. If King Charles does the job well, people will warm to him, and defend the system. The reason the House of Lords is still in place is not because you can really defend it on principle, but because it turns out that it works better than all the other options, short of ripping up the whole basis of the political system.

There are plenty of arguments for the institution of monarchy from a romantic, traditionalist, and even pragmatic basis, but precious few on logical grounds. And since that’s the case, the moment you have a bad, or even merely unsuitable, person in the role, the whole things looks very shaky. Still, it’s trundled along for millennia, so it may have plenty of life in it yet.