We hear this idea pop up every now and again, and I'd thought by now it had been shown to be pointless enough times that no one would seriously consider it again. Apparently, I was wrong. UK Prime Minister David Cameron is considering requiring adults who want to see porn online to "opt-in" by getting what is effectively a "porn license" to surf the sites deemed naughty by the government. Those in the UK government who actually think this is a smart idea might want to talk to their friends Down Under. Australia has toyed with similar ideas in the past, and they've all gone down in embarrassing flames. There was the filter that blocked educational sites, but left plenty of porn available. And there was the filter that took a teenager all of a half hour to crack.

Both of these highlight the key problems with the plan. Once you go down the path of censoring the internet, suddenly very, very big questions are raised about what gets put on the censorship list. It's easy to say "oh, well, porn is blocked," but something countless people (including judges) have struggled with over the years is how to precisely define porn. It's not nearly as easy as many people think. In nearly every case with filters we see a pattern: perfectly legitimate content that almost no one would consider to be porn gets blocked. And tons and tons of "porn" isn't blocked. Second, people will very, very, very quickly figure out how to get around such blocks.

The other issue, which doesn't come up as often, is the sheer ridiculousness of requiring people to effectively announce to the government that they want to view porn. They describe it as an "opt-in," but as I've said in the past, it's really more of a "porn license." People may have all sorts of reasons for looking at porn, but having to tell your government that you want to look at porn seems like a clear attempt to humiliate people for no reason other than that some in the government don't like the fact that others like porn.

If there's concern about kids viewing porn - often the "think of the children!" justification that we hear - there's nothing stopping parents from putting in place their own filters (which are likely to be as effective as any national filters). Why go further and try to block things for everyone?