Using a 22 caliber round on a big game animal is not ethical nor should it be preached. 24 caliber should be the absolute minimum. I don't endorse it at all.
I don't endorse using .22 calibers on deer either, but I would not go so far as to claim all .22 cal rounds are unethical. Explain to us how it's unethical? There are different types of .22 caliber bullets. We're not talking .22LR here. I've been hunting biggame long enough and have taken enough biggame over the last 26+ years to know that using a .223 is not unethical as long as you do your part. As I've said before, it doesn't matter what caliber or cartridge you use, as long as it has enough velocity and energy on target to reach the vitals and deliver a humane kill. Every hunter has to do his/her part to ensure a clean humane kill no matter what cartridge they use. I've seen guys get buck fever on deer using stuff like .30-06 and 300 win mag, yet their gut and rump shots were just as unethical because they could have done a better job at hitting the damn thing, but instead they let human emotions get in the way of what could have been a humane clean kill. Ethics in hunting are not just about caliber size, they're a pretty broad subject. I know for fact that a .223 and .22-250 will for sure give a clean kill on deer, but like all cartridges it has it's limitations and all hunter need to be aware of those limitations. I myself use .270 Win on all my biggame, but I once had some overly enthusiastic novice try and tell me that using a .270 Win on elk was unethical Of course the guy was 17 years younger than me and had up to that point never even been on a hunt before.