It would be an easy vote to say "no porn in libraries." But mountains of documentation show that you can't screen out porn without screening out lots of sites with words like "Dick Cheney." The Supreme Court recognized that filters are far from perfect. Filters are based on keywords. Image recognition software for this still blocks out chimpanzees, babies, art etc. and is even worse than keyword software.
That's why the Supreme Court said that although it is Constitutional for Congress to require libraries to use filters (at least those libraries that get certain federal discounts and grants), the libraries must disable the filters on request by an adult patron. For more detail, see an article I wrote for First Monday.
The Phoenix City Council, however, voted to require all filters all the time. If someone has a link to the ordinance, please send it. This restrictive measure is ripe for a lawsuit. Meanwhile, I guess everyone in Phoenix will have to find full Internet access elsewhere.
See Phoenix may end up in court after banning Internet porn in libraries -news entry by Brandon Smith at Jurist.law.pitt.edu