The San Francisco Public Library has the right idea about offering unfiltered Internet access. When you connect to the open wifi network, you’re given this notice and the ability to click right through:
San Francisco Public Library is committed to providing free and equal Internet access to the public without filtering content. We do, however, ask that you respect your fellow library users and refrain from viewing obscene, offensive, harmful matter, or illegal materials prohibited by law.
There may be some uncertainty about what the future of public libraries looks like, but everybody ought to agree that it involves sticking to their core values of free and private access to the information of the world. Asking patrons to be respectful of the other people in the library is a good thing; imposing rigid software-based filters is not.
That’s why, while I personally think it’s not a very great idea to watch porn in a library, the Seattle Public is correct in not installing filters or otherwise censoring what people are allowed to access.
That’s the right idea even if we assume these are perfect filters that have no false positives and no false negatives. As Cory Doctorow has pointed out in a compelling criticism of UK censorship efforts, that’s never the case, and the collateral damage can be dramatic.
Even in places where there’s not the same institutional commitment to free access to information, it’s rarely effective and frequently frustrating to start censoring a list of sites or even arbitrarily defined categories of sites. For example, it’s hard to justify the US Patent and Trademark office blocking EFF’s site, among others, on their guest wifi, and airlines are behaving a bit silly when they install filters on their inflight wifi.