The derogatory expression idiot fringe designates a minority group (especially members of a political movement or adherents to a set of beliefs) regarded as eccentric, extremist or fanatical—or simply stupid.
—Synonym: lunatic fringe.

The expression idiot fringe occurs, for example, in Blitz on speeding, by Peter Kennedy, published in the Solihull Times (Solihull, Warwickshire, England) of Friday 10^th April 1998:

SOLIHULL Council is launching a blitz on drivers who endanger lives by speeding.
A new campaign aimed at persuading drivers to cut their speed in the borough will start on May 12 and last for six weeks. […]
[…]
Conservative spokesman on the transport and highways committee Ron Herd said: “The campaign is aimed particularly at the small minority of drivers—the idiot fringe—who take no notice of speed limits and drive at 60 miles an hour or more all the time.”

But, originally, the expression idiot fringe denoted—and intended to ridicule—a woman or girl’s hairstyle in which the front is cut straight and square across the forehead.

The earliest occurrences of this expression that I have found are as follows:

1-: From Fashionable Frivolities in Paris, written from Paris, France, by “an occasional correspondent”, published in The Daily News (London, England) of Saturday 15^th March 1873:

One of the insensate things decidedly out of date is “the idiot fringe.” Those who wish to limit their foreheads to the depth of the eyebrow should make use of curling-irons, and keep the Roman Empresses in their heads.

2-: From one of the unconnected paragraphs making up the column Brief Jottings, published in the Portland Daily Press (Portland, Maine, USA) of Thursday 24^th April 1873:

The “idiot fringe” is making its appearance quite generally upon the heads of our ladies.

3-: From one of the unconnected paragraphs making up the column In General, published in the St. Albans Daily Messenger (St. Albans, Vermont, USA) of Saturday 26^th April 1873:

“Convict style” and “idiot fringe” are the appropriate and suggestive names applied to two of the present styles of arranging the front hair.

Early variants of idiot fringe include:

– The expression idiotic-looking Vandyck fringe ¹ in New York Fashions, published in Harper’s Bazaar. A Repository of Fashion, Pleasure, and Instruction (New York City, New York, USA) of Saturday 12^th July 1873:

The Pompadour roll, high above the forehead, is out of favor for all except very blonde and prematurely gray hair; also the idiotic-looking Vandyck fringe falling almost to the eyes, in Skye terrier style.

¹ This is, perhaps, a reference to the Flemish painter Anthony van Dyck (1599-1641).

– The expression idiotic forehead fringe in The Fashions, published in the Reading Times and Dispatch (Reading, Pennsylvania, USA) of Thursday 24^th July 1873:

The pompadour roll is no longer worn by fashion devotees, and the idiotic forehead fringe are [sic] to be entirely abandoned.

– The expression idiotic fringe in The new bonnet at church ², published in The Stroud News, and Gloucestershire Advertiser (Stroud, Gloucestershire, England) of Friday 19^th September 1873:

What pains the little maiden is, that you will ever find
In every Sunday service but an echo of your mind,
And that very little head filled with little airs,
You’ll never get a blessing from sermon or from prayers.
Whilst with “idiotic fringe” † in front and chignon stuck behind
In size proportionate, a want of common sense you’ll ffnd [sic].
† The short hair hanging down the forehead, so named by the French.

² This poem was reprinted from “an American Church Journal”—which I have not succeeded in tracing. The poem itself is an expanded version of What the choir sang about the new bonnet, by Harriette Hammond, published in Our Young Folks. An Illustrated Magazine for Boys and Girls (Boston, Massachusetts, USA) of April 1872.

The earliest occurrences that I have found of the expression idiot fringe applied to a minority group are as follows, in chronological order:

1-: From Song Poets Sad, published in The Helena Independent (Helena, Montana, USA) of Saturday 27^th August 1927:

It is said that a successful moving picture play must be broad enough in theme and treatment to get approval from the people who think and also the idiot fringe, with all the people between.

2-: From the column Down The Spillway, published in The Sun (Baltimore, Maryland, USA) of Wednesday 27^th June 1928:

Last night I sat in a hot and crowded theater and saw what has been called a “hot weather” play. Why is it that every summer we are expected to put our brains on ice and go in for “light reading” and all other “light” things? […]
Anyway, I watched the dreary play through, marking its decadence in taste and feeling, its silly emptiness. […]
Yet the audience liked it immensely. Roared and laughed and snickered and stamped its feet, forgetting hot weather. This, I assume, was a “normal” audience. But normal as humans? I hate to think so. On the so-called “idiot fringe of Greenwich Village” I have seen persons I should trust for sanity to a greater, much greater, extent.

3-: From the Liverpool Echo (Liverpool, Lancashire, England) of Saturday 21^st September 1929:

Mr. Fred Eastman, professor of religious literature and drama, Chicago Theological Seminary, University-avenue, Chicago, writing in “The Times” on Americans and their wealth, says:—
“[…]
“Without doubt, many American industries are enjoying a period of prosperity, but that prosperity is neither so general nor so well distributed as to give basis for the English belief that poverty and struggle have become strangers to the United States.
“On the contrary, we have more than enough of both. We have, to be sure, an idiot fringe of rich fools who come to Europe and squander their money in all sorts of ways—but it is a pity that the American people as a whole should suffer because of the antics of such.”

4-: From an editorial about William H. Murray (1869-1956), Governor of Oklahoma from January 1931 to January 1935, who had just caused the arraignment of two policemen on charges of first-degree murder in the matter of the killing of two Mexican students—editorial published in The Blue Valley Farmer (Oklahoma City, Oklahoma, USA) of Thursday 18^th June 1931:

Governor Murray undoubtedly will draw down some harsh criticism from the idiot fringe of voters who always are quickest to break into vituperation of persons who fly in the face of their prejudices, but he has won the admiration and respect of thinking people both in the United States and Mexico. And, incidentally, though many Americans don’t know it, there are a lot of thinking men in Mexico.