I have been shooting long guns for the past 10 years in the military. IMO I don't think that the caliber of the ammunition is the ethical question here. It has to do with the skill of the shooter and shot placement. We usually use a .308 or .300 for all our long range stuff...out to 800+ meters .. some longer. At that range you are getting into environmentals (wind, barometrics etc) and skill of the shooter. I was amazed as to how much effect the wind can have on a .223 round...obviously lighter....the wind pushed the round at least 6 inches in a 5 mph wind at 300 meters...there are formulas for this....Now ethically would you take a 300 meter shot with a .223 round knowing the effects the environment (including shooter stability and position) can have on the bullet? I would be a little hesitant and maybe wait for the deer to move a little closer. With a .308, no problem...but I would pick the high percentage shot...shoulder or right behind it...I have more room for error to still hit vitals etc...My whole point is...the ethics is in the shooter and shot placement not the caliber of weapon. Just my .02!