All I can tell you is of my experience.
My dog was debarked by a very experienced vet who works for breeders all over queensland. If you are having dogs debarked in Qld then my guess is that you may be seeing the same surgery. The reason for the cicatrix in this case is because the surgery removed both sides of the bellows, not just one, leading to the base of the wind pipe being slightly nicked. This is doen when the owner wishes the dog to be made VERY quiet and is not the norm these days, however my dog is not yet 4.
This complication does occur in a small percentage of cases as i said - I have done extensive research and spent an hour at Queensland University with a canine specialist having the reason for the cicatrix, the different surgery options and physiological reasons for explained to me in great detail before her last corrective surgery. I could not agree more - it is very unlucky - what i would like to point out is that it does affect a quantifiable percentage of dogs. If your dog is a saluki or other breed that is very sensitive to anaesthetic this is a strong consideration.
As for the lack of confidence, I guess that depends on the drive and breed of your dog, the understanding of the trainer you work with and how much training and of what nature you choose to do with your dog. For those only interested in obedience trainng it would not be an issue. For those whose dog is not dominant my guess is it wouldn't be either - but that is an unqualified guess.
Debarking is a personal decision for pet owners, whose criteria for such a decisison are defined by their personal living situation and the type of dog they have. Given my dog's experience and the fact that my breeder and several vet's are aware of the complications I feel that it is relavent information for anyone considering debarking their dog.
Finally, and I am sure some of you will not agree with me and that's ok, I think people see debarking as a convenient way to solve their dog's barking problem - without taking other steps to encourage alternative behaviours.