Back at my highschool, some while ago now. We had a filter system put in. It would prevent us from doing proper research for school. For example, if you were doing a project on World War 2, say good bye to any page that has the word Hitler in it, Death or variations thereof.
It also did a good job of blocking sites that I can't really complain about; hate groups, etc. But it had the reputation of blocking perfectly innocent sites too.
Now, here's the kicker. The filter wouldn't let me go to a perfectly innocent site I go to frequently, but, I was still able to go to the Glock Firearms website.
It all kind of went downhill from there.