There was ALWAYS some limitations on books made available to children - even the Chicago Public Library had a policy of not letting children check out books from the adult section of the library, which AFAIK back when I was a kid did not have the kind of pornographic materials at issue today.
One of the funniest things I saw on the news regarding this issue was a concerned parent at a school board meeting reading - or attempting to read - directly from a book the school library was making available to 3rd graders. The news story had to bleep out quite a few words in the film clip, and the school bureaucrats demanded he stop with the foul language.
The school bureaucrats were outraged - not that the book was in the schools, but that the parent was blowing the whistle on them. Which says a lot - none of it good.
I really don't care what adults read - it's none of my business. But there SHOULD be some limitations on what's provided to children. We don't sell them alcohol, tobacco, or firearms, so we shouldn't provide porn (normal or alphabet type) either.