Thanks, folks, for all your explanations, but I am still somewhat dissatisfied.

If I needed to block out external noise for any reason, I'd probably place the palm of my hand over my ear. It's more comfortable, more sanitary, less disgusting to onlookers, probably more effective (though I haven't done a lot of tests), and would serve as a signal to the noisemakers to "pipe down!" (Where does that expression come from, by the way?) In fact, this method seems so natural to me that it would never occur to me to use any other.

As for the radio announcer technique – this must date back to the days before radio announcers wore earphones. I can't remember where I learned it, but I thought it worked like this: Place the finger tips gently on the outer edge of the ear, bend the ear forward so as to extend it outward from the head to the maximum extent, and hold the fingers palm of the hand parallel to the cheek an inch or two away from it, with the heel of the hand near the mouth. This will form a channel that conducts sound from one's own mouth to one's ear. (Dave Bryant: Is this what you mean by "foldback?") I see the benefit of doing this, BUT – it seems to me that if you did it enough while practicing at home, you wouldn't NEED to do it in public. You'd already know what your voice sounds like. Anyway, it's not the same as sticking your finger in your ear, and not likely to be confused with it.

Several people have stressed that there are good, practical reasons for the FIE. If so, why is the technique so often mentioned with scorn (as in the quotes in my first post)?