We have this issue now. We currently have filters setup on our public computers, but it doesn’t completely prevent people from viewing sites with adult content on them. Unless we remotely access the computers or someone complains, we can not see what the patron is viewing. Its a difficult position to put our circulation staff in as they are the ones that have to monitor the computer usage. Most of the time, a redirection towards proper behavior is enough (“Sir, there are children present in the library and that is not the most appropriate material to be viewing publicly.”).
People are very creative with their “adult content” viewing though. We have several patrons that use YouTube (VS bra advertisements, pole dancing competition videos, work out videos) and FanFiction sites. These same patrons enjoy checking out erotica (Zane mostly) and have found out that Negima contains fairly graphic images and adult situations.
As far as the freedom of speech aspect, I agree that it should be protected. In Missouri, however, we have policies that regulate the the public display of offensive or sexually explicit materials (RS MO-573.060) and this allows us to revoke computer privileges for the display of sexually explicit materials on the computer. The library system is also required by CIPA (Children’s Internet Protection Act, PL 106-554) to have filters on all library computers so that minors are protected from viewing sexually explicit materials. Individuals (17+) can request that the filters be removed, but when we remove the filters we will be able to see if the site is suitable for the patron to be viewing. These “Internet Acceptable Use Policies” are posted next to every computer and are available upon request for any patron that asks.
Missouri has some fairly tough laws on cyber porn and it helps to have these laws backing publicly funded libraries!