"Barely educated simpleton" is unnecessarily harsh. Historically speaking, living in an era with majority literacy is unusual (so as to dodge questions about the "true" level of modern literacy), as is living in an era with large numbers of people with the free time to read anything.
It is true that Dickens could assume a somewhat higher level of IQ in his readers of the time than we can today in books targeted for the "average" reader, but I think most of us would consider that an unfortunate thing if we really thought about it, rather than a virtue of the age.
If you want challenging books, there's no shortage of them today. You just need to know where to look.