Just because it exists doesn't mean the libraries are OBLIGATED to make it available. Nor should they be.
They aren't obligated to make it available, but neither are they allowed to NOT make it available on censorship grounds.
And I guarantee, if you make free porn in libraries a "right" then the libraries will be flooded with the most depraved individuals imaginable. People who want to look at porn without being detected, and who at the same time want to prey on children.
People who want to look at porn without being detected...do it in public spaces?
Umm, ok then.
Oh yes, and think of the children.