The library system in the nearest city to me started by putting filters on the computers in the kids’ section and nothing on the rest of the computers. Then in 2007, the library board decided at a meeting without even putting it on the agenda to put filters on the adult computers. Then things blew up. Very much in the same way that the debate is going in the UK actually. The busy-body Christians and the anti-porn feminists on one side against the librarians, freedom of expression people, and technical people who know that filters are useless on the other side. The filters were removed after a few more library board meetings and physical privacy screens added to make accidental viewing of other peoples screens less likely.
While I was checking for articles to see if my memory was accurate about the events (it wasn’t entirely), I found this really good video from 2011 about what happened. It’s an hour long presentation at Western University from one of the free speech people. (It also contains a partial shot of what I think is one of the Abu Ghraib photos, so maybe nsfw).