Not all libraries allow access to porn. I used the library computer in Sturgis, SD and the guidelines and restrictions were spelled out in the user agreement stating porn sites were blocked.
The library in my county in Wyo also does not allow access. I was reading newspapers when I heard a fella asked why he couldn't access a certain site. The librarian told him it was blocked, as were all similar sites, since they could be viewed by other patrons and he was welcome to find another free internet service.
Both places also limit a person's use to 30 minutes daily.
They don't all do that?!?
PS - the DU OP is a major waste of their mother gaia's resources, IMO.