It's a surgical procudure - and I cannot believe they would do it to show dogs.
Debarking - This procedure involves the removal of 2 folds of tissue located on either side of the larynx or voice box in the dog. The so called vocal folds
actually function to come together in order for the dog to make an audible sound with pitch. When removed, the sound made by the dog is much like that of a
whisper, or a bark heard from far away when the dog is right next to you. The effect of debarking can be explained much like an individual trying to whistle while
the lips are apart. In order for sound to occur, air must travel through a narrow opening in either the voice box for a bark, or the lips for a whistle to occur.
I imagine not only does it hurt initially, it probably confuses the heck out of the dog when he's trying to sound the alarm and be helpful to you, but he can't!

I would never de-bark a dog, and doubt that folks who love dogs enough to show them would either.