After yesterday's post about "the way things were" I thought of one more subreason why this isn't always a strong argument.
I've been reading the Game of Thrones series, as have many folks in my general set of friends. For those of you who haven't read the books, they're set in a psuedo-middle ages fantasy realm (summer lasts for 9 years, dragons exist, etc). Anyhow, twice in the past few months I've gotten in to a discussion about the books in a group and had someone mention "how awful things were back then". Each time of course, someone pointed out that these books are not historical fiction and not meant to be an accurate representation of any time period. Of course the person making the mistake laughed.
These are not intentional gaffes, but strongly written fiction can convince us we learned something about a way of life that may or may not have existed.
It's often mentioned in Christian circles that more of our visuals of hell come from Dante's Inferno than from Biblical description.
The point is, when you have a strong picture in your mind about a time period, make sure it didn't just come from a good book.