I am strongly anti-censorship, but I also willingly accept that there are limits regarding generally-accepted bounds of behaviour. Shouting "fire" in a movie theatre is the classic example of justified censorship. I think Canada is very generous in its definition of what those bounds are. Ontario moreso than even most other (very liberal) Canadian provinces.
The problem I have with the "porn in the library" scenario is that children in the library could very easily see screen shots that they should not be exposed to. As adult citizens, while it is of course not our job to raise strangers' children or to define the (legal) content of what they can be exposed to (that's mom and dad's job) it is our responsibility to protect Canada's children from what a normal, rational person would consider inappropriate. I think that even on a prostitution-related website like TERB, most of us would agree that children should not be exposed to pornography. Viewing escort websites on a library computer could very easily expose children to pornography, and so it should not be done.
That said, I am also not a fan of women breastfeeding their babies in public. Masturbation and defecation are normal, healthy physical acts that everyone does. Behind closed doors. And that is where breast feeding and surfing porn belong too.