Red Hen, from what I've read, breathing CO2, in the correct proportion, will cause an animal to lose consciousness, like fainting or suddenly passing out. They continue to breathe, so it's not like an asthma attack, or having your airway blocked. They wouldn't know there's no oxygen in what they're breathing. I thought maybe a chunk of dry ice in a box, put in the bird, cover the box, wait a few minutes. Or a jar of peroxide in a box, put in the bird, drop some baking soda in the peroxide, cover the box. Why anybody sees this as a great danger is beyond me.
Shooting a bird in the head, as I think of it, on a stump or wood block, gun pointed down, and at point blank, also seems very quick, easy, and sure. It you had two nails in the stump to hold the head, I'd think it would be pretty straight forward. Again, why some people see this as a great danger, I don't know.
I have sliced myself, more than once, in the process of slicing that loose neck skin to cut the throats. And, they didn't die quickly that way, either. It took several minutes.
I'm not sure I have the coordination and hand strength to hold a bird and wield an ax at the same time.
There is no place near me to take birds for processing, nor could I afford to add that cost to the cost of raising my own birds.
I can't speak for anybody else, but I don't have a problem with killing them at all. I've killed several. I just want to do it as quickly as possible. That, I've encountered problems with, and I'm trying to correct that.
Why anybody seems to have a problem with that idea, I don't know.