The one time the issue of filtering content in libraries made it to the Supreme Court, it barely got upheld, and that was a filter that people 18 and over could have disabled on request (US v. American Library Association). Of course we don't want explicit content on display where bystanders can be exposed to it. However, I'm hesitant to hand the power to decide what is and isn't appropriate to government employees, especially in the context of library computers, which are the only access point to the internet for many people.