The day after Oz and Ends's weekly Robin segment entered upon the tough question of superhero garments, the 10 March issue of The New Yorker appeared, bearing novelist Michael Chabon's reflections on the same topic. He even makes one of the same points I did: "Robin’s gaudy uniform hints at the murder of his circus-acrobat parents." So I can't resist the urge to assert some primacy by commenting on Chabon's remarks.
He begins by recalling a difficult moment in his religious-school lessons in "Jewish Ethics":
The one time I felt my soul to be in danger was the Sunday Mr. Spector raised the ethical problem of escapism, particularly as it was experienced in the form of comic books. That day, we started off with a fine story about a boy who loved Superman so much that he tied a red towel around his neck, climbed up to the roof of his house, and, with a cry of “Up, up, and away,” leaped to his death. There was known to have been such a boy, Mr. Spector informed us--at least one verifiable boy, so enraptured and so betrayed by the false dream of Superman that it killed him.
This story made a brief appearance in Frederic Wertham's influential 1954 anti-comic book manifesto,
Seduction of the Innocent. Wertham summarized (without identifying details) an article that
Time had run on 22 Jan 1951:
"I Almost Did Fly." According to the news magazine, however, the caped hero who tempted six-year-old Dickie Bonham to his doom was not Superman but
Mighty Mouse. That mouse had appeared in animated cartoons before entering comic books, but neither the magazine nor the doctor dared to suggest to Americans that movies were inherently harmful.
Chabon's main point is:
like the being who wears it, the superhero costume is, by definition, an impossible object. It cannot exist.
Exhibit A in his argument is folks who attend comic-book conventions in cosplay mode. Even fans who
dress up successfully can't replicate the eye-popping perfection of illustrations, and it's best to stay away from the
other end of the
cosplay spectrum. (What did I just tell you?)
But Chabon stumbles when, seeking to arrive at the skin-tight unitard or even the naked muscular form as the essence of superhero costuming, he tries to dismiss the cape by dropping one anomalous, self-parodying example:
Capes have been an object of scorn among discerning superheroes at least since 1974, when Captain America, having abandoned his old career in protest over Watergate, briefly took on the nom de guerre Nomad, dressed himself in a piratical ensemble of midnight blue and gold, and brought his first exploit as a stateless hero to an inglorious end by tripping over his own flowing cloak.

Captain America had no experience dealing with a cape, of course. If Chabon wanted a fair consideration of what "discerning superheroes" think of capes, he should have asked one who wears the garment what the essence of a hero's costume is.
In fact, even though not all superheroes wear capes, the garment is so closely associated with them that in much of the superhero universe cops and cynics use "capes" as a term for all costumed heroes. In our world, Dickie Bonham certainly understood where superpowers could be found. Even Chabon's final anecdote involves a towel tied around the neck at one end.
The very fact that capes make no sense is why they (along with muscle-displaying tights or bare skin, to be sure) are the essence of superhero costuming. FDR aside, they were past fashionable when Superman showed up in one in 1938--ensuring that he had a special, out-of-this-world look. They're highly impractical, as
The Incredibles discussed. Even when comic-book creators try to provide a reason for a cape, as in Batman's
cheiropterous disguise, we all know the real reason for one is simply that a cape looks cool in the artwork. Real capes never drape or flutter the same way, alas. But a superhero costume is symbolic from the start; "it cannot exist," as Chabon says, but it's not really supposed to.