What's the difference between Madeleine McCann and Pope John Paul II? You won't go to prison for telling jokes about Pope John Paul II.

Admittedly Matthew Woods, who has been sentenced to 12 weeks in prison for his comments on Facebook, didn't only make jokes about Madeleine McCann - he also made light of the disappearance and tragically likely death of April Jones.

It's probably the latter that was responsible for his upcoming time at Her Majesty's pleasure. The jokes weren't funny, and making them while the case is so raw was always likely to have some sort of backlash if they found a wider audience, as he found when a 'vigilante mob' showed up at his house.

Woods doesn't seem like a particularly sympathetic character - according to the Evening Standard, he smirked when he was led from the dock. But whatever you think of his sense of humour, you have to question the constitution of whichever member of the public found what he said (and I won't repeat it here) so distressing.

This would be very different had he deliberately directed them to April Jones's family, but so far there's no suggestion he did, or even that they've seen them. The court case, sentence, and resulting coverage, of course, makes it far more likely that they will. Instead, members of the public reported him to police. Those members of the public, well-meaning as they almost certainly are, need to grow up.

I've yet to find anyone who agrees with the sentence itself, which is ludicrously harsh and will presumably be overturned. But some people have defended his conviction on the grounds it's similar to shouting the comments in a public place, which would land you with a public order offence.

It's a tempting analogy, but it doesn't hold. Shouting in public can travel to people who just happen to be in the area at the time, and so is a form of particular carelessness. In contrast, the only ways people would have seen his comments are if they were friends with him on Facebook, or were searching for 'April Jones'. If it's the first, they've made the decision to follow him. If it's the second, well, we'd best all stop making dead baby jokes in case someone who's miscarried overhears.

Facebook (if you don't impose privacy controls) and especially Twitter are strange things: semi-public forums many of us still think of as entirely private. Recent high-profile cases around 'terrorist threats' to Robin Hood Airport, rioters, and racism towards footballers have thrust social media and the law into the ring, and they're still warily circling each other.

The current situation can't hold. Matthew Woods is not the only person who's made April Jones jokes, and he's not the only one to have done so from an identifiable social media account. He might just have been the only one unlucky enough to have been spotted and reported.

But even aside from the arbitrary nature of his prosecution and the bizarrely strict sentence he's received, this is a prosecution that should never have been brought. Matthew Woods was crude; that someone can be imprisoned for making the wrong joke at the wrong time is what's really offensive.

Follow Jamie Thunder on Twitter: www.twitter.com/jdthndr