Thanks, brekin. I had no idea that some public libraries were like that. Our public library outright censors such sites from access. (My only initial problem with that was, "What other sites are also being censored?" But when I decided to look, everything but porn seems available.)
Although I see pornography as a free speech issue, and think that those who want access to it should be free to view it on their own as they choose, I also think that public libraries (and taxpayers) have positively no obligation to supply the material.
(And anyone who wants to look at that stuff in a public library needs his head examined.)
What I remember was quite a few libraries choose not to be in compliance with something like a Child Internet Protection Act because most of the required filters at the time were over-censorious or didn't really work and so the gates were (are) left wide open. The Library I worked at chose to have some filtering for the Children's Library wing though.
Quite a number of the people who did openly view the stuff were homeless and/or mentally ill. Before they went to an automated timed system there were quite a few verbal and physical fights over people cutting or going over their allotted 1 hour. I'd say for most the free hour of porn was the highlight of their day.