Well actually the co2 does not kill them instantly. It basically puts them to sleep and then suffocates them. The whole process takes a few minutes.

When a snake constricts a mouse, it is very similar except for the sleeping bit. It suffocates to death, but it normally takes under a minute for the mouse to expire.

I don't have a problem with feeding frozen, and I don't have a problem with feeding live. But if you think it is cruel to feed a mouse to a snake, then no matter which way you do it, it is still cruel. In the end, the mouse still died to become food.

I am glad that you are okay with f/t though and that your snake takes it willingly

I wouldn't want to feed my animals wild caught prey...who knows where they have been and what they have eaten.