Do note that you've dredged up a 6 year old topic and that the original poster is not likely respond. CO2 chamber is the general consensus with most breeders.
I was correct in my assumption that some netiquette nazi might make an issue out of the age of the thread. I think it's safe to assume that you aren't a fan of old books then and are probably yourself a youngster?
The age of the thread is a pointless and irrelevant argument. The information is obviously there to be found, and so responding to it for educational sake is appropriate...unless you want to start taking down 6 year old threads? I assume there is a good reason why "old" threads are left up here, or should I throw out my 6 year old copy of Reptile Medicine and Surgery by D. Mader?
As to what breeder consensus is, I couldn't care less. Breeders aren't particularly knowledgeable in this topic and it's not their area of practice. I'm a rehabilitator who has to euthanize injured and ill wild reptiles as a matter of profession throughout the Spring, Summer, and Fall months. Snakes and turtles hit by cars, lawnmowers, attacked by dogs and cats, garden hoes and shovels...I do this as a matter of a way of life as a wildlife rehabber.
CO2 is appropriate for mammals and birds, not so much the case with reptiles who are known to be able to hold their breath for quite some time. Again, they can survive hypoxic conditions for a very long time due to their metabolism, so your breeder consensus is not well grounded. It may be more humane than cutting off a head or using a freezer, but if you are advocating CO2 being a great and recommended way to euthanize a herp, then you just don't know what you are talking about.
The consensus among KNOWLEDGEABLE rehabbers and veterinary professionals is that injection of chemical anesthetics and sedatives are the way to go, and in some cases isoflurane, but THESE people, not breeders, should be relied upon for that opinion. CO2 can be used if you have nothing else, but don't act like it's cutting edge or something. It's just what's most conveniently available to breeders who aren't rolling any of their money into keeping a vet on retainer who could give you some iso or pentobarbital for next to nothing once he knows you.