Harry Potter is like football. I'm talking about the literary, cinematic and merchandising phenomenon, not its focal fictional wizard. He isn't like football. He's like Jennings after being bitten by a radioactive conjuror. But, as with football, reports of Harry Potter-related events, products and personalities are everywhere. Like football supporters, Harry Potter fans seem to have an insatiable desire for more news, chat and retail opportunities related to their enthusiasm. They're standing in a monsoon screaming: "I feel so dry!" while the rest of us are getting soaked.

Illustration by David Foldvari.

It's bizarre. It has the intensity of a fad but it's been going for 14 years. I think I'd find it easier to understand if I hated it. At least that would be an emotion of equivalent strength to the fans'. But, for me, it doesn't conform to the Marmite model: I've read three of the books and seen three of the films. I quite enjoyed them. I liked the third of each no less than the first two. I didn't feel the series had "gone off". It was just something that I only liked enough to consume so much of. It seemed perfectly good but I'd got the idea. I didn't mind not knowing what happened.

And then, obviously, because I am perverse, I was put off it by its ubiquity and other people's enthusiasm. Others' loss of perspective about its merits made me lose my own. Maybe I was trying to lower the average human opinion of the oeuvre closer to what it deserves by artificially forcing mine well below that level. Incidentally, this is where the parallels with my view of football end: even if that were a struggling minority sport only played by a few hundred enthusiastic amateurs, I would still consider it an overrated spectacle that lures vital funding away from snooker.

The most amazing aspect of JK Rowling's achievement and that of the Harry Potter marketing machine is that they have produced so much stuff for so long – kept the profile so high, the advertising so pervasive – and yet somehow contrived to leave a huge section of their audience still wanting more. They've given Harry the attributes of pistachio nuts and crack cocaine without the health risks (opening thousands of pistachio nuts can cause severe thumb-bruising, I can tell you from bitter experience of my life on the edge).

But, with the launch of the new Pottermore website, are they finally pushing their luck? Since last week, trial access has been granted to a select group of a million fans. That's the real hardcore. Having a Harry Potter tattoo won't be enough – it has to be on your face. The site boasts material that didn't make it into the books, such as 5,000 words about which woods should be used to make magic wands and anecdotes about where Rowling found inspiration: why she called an unpleasant character "Petunia", for example. But a fan writing in the Times wasn't impressed: "As a reader who has grown up with Harry over the years, the site dispels the magic of the wizarding world by removing the air of mystery behind the narrative that sparks debate among fans."

That's an attitude that strikes a chord with me and reminds me of Star Wars. Every generation must lose its innocence, must see the brightly painted nursery wall smashed away by the wrecking ball of betrayal to reveal a blighted landscape. For our predecessors, it was the Somme, the Great Depression, the Holocaust or Vietnam; for my generation, it was The Phantom Menace.

The problem isn't just that it's terrible but that it also retrospectively spoils the original films. George Lucas took the hinted-at mythical, ancient yet futuristic realm of his first films and filled in all the detail like a tedious nerd. He ruined his own creation. It was as if Leonardo da Vinci had painted a speech bubble on the Mona Lisa in which she explained her state of mind. Everything that was magical, mysterious and half alluded to, he now ploddingly dramatised, making it seem dull and trainspotterish. Those three prequels worked like aversion therapy for my addiction to the franchise.

I'd wanted the prequels to be made – I'm sure most fans did. We were desperately keen for Lucas to answer all the questions that the original films had posed. But he was wrong to accede to our wishes – not financially, but artistically. When it comes to art and popular culture, consumers are like children and chocolate, students and alcohol: they don't know what's good for them, they can't predict when certain behaviour will make them feel sick.

As with junk food, so with books, films and TV, the current trend is to give people what they think they want, rather than to leave them wanting more. Presumably that's the motivation behind making a new episode of Inspector Morse featuring the character as a young man. ITV knows that fans of Morse will watch it (God knows, they watch Lewis). The original series brilliantly hinted at the character's troubled, melancholy past, so we'll tune in to find out the details.

It's like with a magic trick: you're desperate to know how it's done but, when you find out, the mundane truth usually disappoints and undermines your enjoyment of the illusion. Similarly, the specifics of Morse's past can't possibly live up to our imagined versions. Like a good magician, ITV and Colin Dexter would serve their audience better by resisting its curiosity. Fans don't really know what they want or they'd make up stories for themselves. (Some do and "fan fiction" is an excellent way for them to slake their thirst for content without destroying the mystery for everyone else.) With a story, as with a well-chosen gift, we're happiest when surprised by something we didn't know we wanted.

So it annoys me that there's such pressure to provide more backstory and more information about films and TV. DVDs are packed with deleted scenes, out-takes, "making of" documentaries and explanatory commentary. The experience of making a TV show today is to be perpetually distracted from working on the actual programme by demands from the broadcaster's website for additional material that will inevitably be of a lower quality. Some of this is harmless, but a lot of it is telling people how the trick is done.

I hope the new Harry Potter website won't undermine the enjoyment of the Potterverse for those million golden ticket holders. But it's a possibility. In the real world, chocolate isn't made in a magic factory by Oompa Loompas. And as for Ginsters slices… there are some things that you just don't want to know.