Filtereing software is very restrictive. If you have ever tried to surf the internet that has been rendered "child-safe" you'd know. The computers at the Liberty Center on the navy base wear I work installed Net-Nanny and so many webpages were blocked that they wound up removing it. Now they just post signs saying if you are caught surfing porn, your CO will be notified. That seems to work a little better.
That is a reasonable policy at a Naval Base's Library, but not for a public library open to school children.
As I posted earlier, I understand that the software needs to be disabled for some very legitimate searches. I just don't see that as an excuse not to use it at all.