Wimp.
Chameleon smasher
Anybody ever see somebody who died of hypothermia? How about death by helium? Suicides in general? I have. Lots of them actually over time.
So many hypotheticals here. Seriously. Popcorn is about the right response.
I for one never want an animal to suffer. However I know getting eaten by another animal has gotta hurt. Despite that, I let nature be nature mostly. If you can't handle nature, don't own a pet.
I don't pre-kill roaches, stick bugs, or nearly anything I feed my Parson. Why? Same reason you all don't.
I don't pre-kill anoles or geckos the Parson actively hunts and eats. Why? Because it's natural and humans shouldn't try to force their viewpoints on everything concerning nature.
I do pre-kill the monthly mouse fuzzy. Why? Because I won't take a chance on hurting my Parson, that's why. It's not for the mouse's needs. If I cared about the needs of the mouse to that degree why own an animal that eats one (I own a lot of boas I should add).
Nature is not nice, she's a mean mean bitch for those of you not in the know. Pain is part of life. Avoid it if you can but don't ever think you can make it disappear.
Now, I've had the occasional shitty experience in keeping so many animals over so many decades like anybody else in the hobby. For my two cents, freezer turned up to max is the way to go if you don't have access to a Vet. You get cold, you lose sensation, you go to sleep, you don't wake up. In the case of a cold blooded animal this is 100%. In the case of people, I've seen the looks on the faces of the dead, I haven't seen a look of pain or discomfort yet in hypothermia cases or the helium ones.
Smashing the little critter to prevent pain? I think you give up a little of yourself if you go that route.
If the owner wants to give keeping it alive a try, well, at least his heart is in the right place. It isn't going to work for a huge number of reasons, but the owner doesn't have the experience to know that so cut him some slack.
Wimp?

Not at all. Never mistake silence for a lack of strength. Emotional topics are not my cup of tea since there is not a right or wrong answer. There is not a solution like knowing which light bulb to buy, but in emotionally charged topics the participants always think there is one. Passions replace practicality.