Cracked offers Five Ridiculous Myths You Probably Believe About The Dark Ages; number one is "The Dark Ages Were A Real Thing":

The Dark Ages were never a thing. The entire concept is complete and utter horseshit cobbled together by a deluded writer. The term "Dark Ages" was first used in the 14th century by Petrarch, an Italian poet with a penchant for Roman nostalgia. Petrarch used it to describe, well, every single thing that had happened since the fall of Rome. He didn't rain dark judgment over hundreds of years of human achievement because of historical evidence of any kind, by the way; his entire argument was based on the general feeling that life sucked absolute weasel scrotum ever since Rome went belly-up.

Likewise There Were No European Dark Ages, The Myth Of The Dark Ages, The Myth Of The "Dark Ages", Medieval Europe: The Myth Of The Dark Ages, Busting The "Dark Ages" Myth, and of course smug Tumblr posts.