My mom was a librarian. She would have helped you find information about how to build a bomb if you had asked. She was not cool with people watching porn in view of others. She would have checked any pornographic book out for you. Most librarians are not cool with people looking at porn in open spaces where it will impact other users. I think most of them would not care if a person was in a secluded space. Internet or no, people love to be perverts in public libraries. Flashers are very common, masturbators a bit less so. Don't know what it is but they love the library.
I worked in a library for five years, as a page. It didn't happen often, but once in awhile I did catch people looking at porn on the computers. I never did say anything to my boss, because I felt squeamish about reporting such things. I regret not doing it now, I agree that watching pornography near others in a public space is an uncomfortable act. As for whether or not porn should be in a public library at all, I'm not quite sure what to think. Is it appropriate to put in a 18+ section of the library? I don't want a main function of libraries turn into providing smut to users. On the other hand, why shouldn't people have access to materials if they want them? Maybe pornographic materials should be available for use at home through a library's site, but not in the actual library? Just a thought.