People say bad things online. They write vile lies about blameless worthies. They pen disgusting racist jeremiads, post gut-churning photos of sex acts committed against children, and more sexist and homophobic tripe than you could read - or stomach - in a lifetime. They post fraudulent offers, alarmist conspiracy theories, and dangerous web pages containing malicious, computer-hijacking code.
It's not hard to understand why companies, government, schools and parents would want to filter this kind of thing. Most of us don't want to see this stuff. Most of us don't want our kids to see this stuff - indeed, most of us don't want anyone to see this stuff.

But every filtering enterprise to date is a failure and a disaster, and it's my belief that every filtering effort we will ever field will be no less a failure and a disaster. These systems are failures because they continue to allow the bad stuff through. They're disasters because they block mountains of good stuff. Their proponents acknowledge both these facts, but treat them as secondary to the importance of trying to do something, or being seen to be trying to do something. Secondary to the theatrical and PR value of pretending to be solving the problem.