OP didn't say "porn bad for children". They said "porn bad".
(At least I'm not aware of any public libraries with adult-only sections.)
And in the context of the overall discussion of a bill attempting to restrict specifically children's (not adults') access to porn.
But since you asked, I'll respond. I have my own computer and internet connection, so I don't watch anything at the library. But it's not unheard of for homeless people to watch porn at the library.