My favorite shot is just behind the front leg, 1/3 of the way up the body. This results in the top of the heart taken off and a entrance and exit wound with a cup and core expanding bullet like a Gameking.
I have taken a head shot though, and it was offhand. The doe popped up in front of me and I had the head to work with so at about 40 yards standing on my hind feet unsupported, she became DRT. Is it my goal? Nope. Can I do it? Apparently. Is it ethical? One shot kill DRT, so yep. Not everyone is a minute of pie plate shooter, not everyone "can't" do it, not everyone substitutes magnum for skill.
I believe that a "ethical" shot changes with the skill level. If you CAN do it, and I mean you really can, every time, then it is a ethical shot for you. To make a blanket statement that X is unethical, be it a +300 yard shot, or a head shot, IMHO is speaking without all of the facts, or making assumptions on a persons unknown skill. Knowing the differance between the shot you can make and the one you cant, is also a skill.
EG my daughter would be unethical to take a 50 yard supported head shot with her 30-30. From a bagged bench, sure, not a shooting rail from a tree stand or a supported field position. The son, with his 25-06, in a field supported position, sure, out to 75 without a problem. I could make the shot with out a lot of trouble supported pretty comfortably to whatever range I can shoot on my property, and I can offhand if the conditions are right at a shorter range. I know a guy who it would not be unethical for him to take headshots at 200 supported, and others that are questionable on the boiler room at 75.