Are tabloid readers just as responsible for the bad behaviour of the press as the hacks and paps? It's a question I've been asking myself over and over while the Leveson inquiry (or to give it its full name, the "Leveson inquiry into the culture and practices and ethics of the press") has been going on.

In a rather poignant reflection of the celebrity culture that fuelled this miserable business in the first place, the appearances of "big names" at Leveson have drawn bigger headlines and longer articles than those of more ordinary, more boring, less photogenic folk. Today's appearance by Sienna Miller will doubtless give the chance for trouser-rubbing picture editors to pore over her features once again. And so it was the case yesterday when Kate and Gerry McCann, the parents of missing child Madeleine, came to give evidence.

The couple spoke of how their privacy was invaded, how their shocked world was intruded upon by photographers and reporters alike, how private diaries were printed without their permission, and how they had to read rumours from police lines of inquiry presented as if they were legitimate versions of the truth. Anyone who has the merest sliver of empathy can only recoil in horror at how the parents of a missing child could feel under those circumstances.

But the hacks and paps didn't descend on Praia de Luz because they were out to get Kate and Gerry -- their privacy was just collateral damage. What they really wanted to do was flog papers -- and this was a story that had produced a reading frenzy, even bumping the Daily Express's traditional sales banker of Diana off the front page. Is it the fault of a profit-making enterprise to want to maximise sales at a time of decline? Or should those who hungrily sucked up the photos and stories of the McCanns bear some responsibility, too?

Nobody knows what sells papers; it's still a bit of a mystery even as the newspaper industry heads towards terminal decline. We can all guess and speculate. You can ask readers, but you will always have to bear in mind that people like to sound more ethical than they really are - who's going to fess up to feasting on trashy celebrity sleaze and intrusion into famous people's private lives, even in an anonymous survey?

But the heat and light generated by certain subjects and certain stories is easier to see now, thanks to the web, where our interests can be easier to see than what we'd admit to reading in a paper. That's why huge chunks of the Daily Mail's website, for example, are devoted to American minor celebrities you've never even heard of wearing bikinis; that's what guarantees traffic.

And that's why there was such a clamour for McCann stories back when the little girl went missing, and why stories about the mystery continue to be popular today. We want to read them, so the search for new angles continues; in that battle for fresh meat, it's not a massive surprise that some journalists will cross the line to get what they want. They do it because we want them to.

Additionally, it was a case that took place in Portugal, so newspapers were left unrestrained by those annoying obstacles of trying not to prejudice criminal proceedings and could say what they wanted while Robert Murat -arrested because the pack of hacks swarming around Praia de Luz decided he was a bit weird - and the McCanns were treated as suspects. It was a chilling glimpse into what would happen without reporting restrictions, a look into a world where journalists could simply write about ongoing cases without thinking of the consequences.

So while Leveson carries on, hearing from victims of phone hacking and journalistic wrongdoing, there's something missing. The other people responsible for this behaviour are getting away completely free of blame, without being scrutinised or having their actions looked at. The other perpetrators are us -- those who bought the newspapers in the first place. You or I might haughtily contend that we are above such things and we don't buy such garbage, but are we really not part of the problem? Do we really not contribute to a culture in which celebrity is seen as the peak of achievement, in which the lines between public and private are being erased all the time?

It would take a long time for Leveson to hear from the millions of people who bought papers because they wanted to read about Celebrity A's lovelife, or the misery of Family B as they were immersed in grief. But we can't pretend they don't exist. Or that we're not part of the problem.