The American Library Association (ALA) is of the mind that there is no such thing as "age appropriate" material (they have stated this explicitly on their website). You are lucky that the works of Robert Crumb (such as Fritz The Cat) were not filed along side it.
While I think that it is valid to have the works of Robert Crumb in a library (completed collected works are available in reprint), I do not believe that they are right for all ages any more than a library should be loaning out R and NC-17/X films to 13 year olds.
But what's the solution? Keep kids out of the adult fiction of non-fiction sections of the library? What if the kid wants to read Orwell or Tolkien? Is it the librarian's job to oversee what a kid is reading or is it the parent's? These are hard questions.
And by the way, the historical romances that many women devour on a regular basis - we call them "fat juicies". Talk about sex!
I thought the "Fritz the Cat" comics were funny when I was in college. But you know, if we wanted that stuff, we went to the "dirty books store" and bought it.