Gary Lachman, author of Turn Off Your Mind writes:

Much has been written about 2012, pointing out both the value and the flaws in Argüelles’s and McKenna’s interpretations. I don’t intend to repeat those here. The strangeness of the ideas did not repel me. At the time that I came across them, I was reading Rudolf Steiner, who had his own prophecies concerning the third millennium, which, to be honest, were rather vague. I had also already spent some years in the Gurdjieff “work,” so odd ideas were not a threat. What troubled me then and today is what I call the “apocalyptic gesture,” a point I raised recently on the Reality Sandwich website, much of which is dedicated to the 2012 scenario. The desire for some once-and-for-all break with the given conditions of life seems, to me at least, to be embedded in our psyche and is a form of historical or evolutionary impatience. Social, political, or cultural conditions may trigger it, but in essence it’s the same reaction as losing patience with some annoying, mundane business and, in frustration, knocking it aside with the intent to make a “clean start.” While in our personal lives this may result in nothing more than a string of false beginnings and a lack of staying power, on the broader social and political scale it can mean something far more serious. […]

The “Summer of Love” in 1967—which by many accounts wasn’t as groovy as believed—quickly became the year of “Street Fighting Man” in 1968, when the “generation gap” promised to turn into something like revolution, and dangerous slogans like “If you’re not part of the solution, you’re part of the problem” promoted a simplistic us-or-them scenario. Yet by 1969 the hopes of an Aquarian Age had been severely battered by the gruesome Charles Manson murders and the Rolling Stones’ disastrous concert at Altamont, when Hell’s Angels murdered one man and terrorized hundreds of others, including the Stones themselves. (I tell the story in Turn Off Your Mind: The Mystic Sixties and the Dark Side of the Age of Aquarius.) Exorbitantly high hopes can often lead to very deep depressions, and in a microcosmic popular sense, within a few years the peace and love unreservedly embraced by the flower generation became the “no future” of the punks. Cynicism, jadedness, and pessimism often constitute the hangover from the intoxication of excessively high expectations. No one rejects ideals more vigorously than a bruised romantic.

Disinfo: 2013: Or, What to Do When the Apocalypse Doesn’t Arrive

It’s not what Lachman is writing about here, but a detailed account of the origins of the 2012 myth can be found in Sacha Defesche’s excellent paper The 2012 Phenomenon.