I didn't read all of the replies, so I don't know if this thread has taken a turn to a different topic or not, but I'll give my opinion on the question that was asked.

Ethical hunting, when considering ANY shot, means you are confident that your shot will end in a clean kill.

My father was a crack shot, but he was never a big game hunter. I'm not sure I ever saw him fire anything larger than a .22lr (although I had heard fables of his ability with the .44mag levergun he carried in the truck).

This is an unethical story, but because of the legality of the weapon used, not the shot placement. When I was in college, my dad and I were hunting raccoons with Jack Russel Terriers one afternoon under a grainery, the dogs were working hard and chasing several coons back and forth around inside the foundation when a herd of deer ran up. A massive chocolate nontypical buck with bases as thick as my wrist was in the mix, standing about 50yrds away staring right at us. "My God", I whispered under my breath, "I wish I had my rifle". (It WAS in season). "You do." My dad whispered back, eyeballing my .22lr Marlin 60. I replied that I couldn't take a shot with my .22. My dad shrugged slowly as he raised his rifle whispering, "I owe you a tag next year" as he slowly raised his open sighted.22lr Marlin 60, took a deep breath, and before I could even object, cracked off a single shot.

The buck dropped like a sack of concrete. Being shot through the eye will have that effect.

While I don't condone it, my dad had no doubt that he could cleanly kill the deer, and he did. Nothing unethical about that. (yeah, the illegal weapon is a different story

Granted I'm not so bold as my father, but I'm a fan of venison, and I'm a fan of using different guns to bring it home. One evening while calling coyotes a buddy questioned my use of a 9mm carbine (kel-tec), since it was "so underpowered". I boasted the number of coyotes I'd killed with it and bragged that I felt it viable for deer even-under the proper circumstances. So the bet was clinched, and later that year I punched a 9mm hole (9mm rifles are legal for deer in Kansas) right behind the ear of a fat doe from 35yrds (I like upper neck shots, high likelihood of hitting the spine, windpipe, and arteries). She dropped with a single shot. Again, I had no doubt I could make the shot cleanly.

I also have a friend that's a terrible shot. His deer hunting weapon of choice is a 6.5x55swede in a sporterized mauser. He's so terrible that he has me sight in his rifle for him, and only to 50yrds. The rifle is sweet, I can get sub-MOA groups to 100yrds with ease, but he knows his 100yrd groups will never be less than 6", so he just will NOT shoot past 75yrds. Ethically, he knows he can't ensure a clean kill at 100yrds.

The moral of my stories is confidence dictates ethics. An inexperienced shooter taking a 150yrd lung shot with a .30-06 that he knows is marginal for his ability is far less ethical than a well seasoned shooter taking a 100yrd neck or head shot that he knows he can produce a clean kill with.