IMO a hunters personal ethics has a lot to do with it. First you have to be competent, which is a lot harder with a bow. Second is you have to be a lot closer, which requires better stalking skills. Thirdly and most important IMO is you have to pick your shot and pass on iffy shots.
An ethical kill, is an ethical kill, no matter what tool you use. I only take the shots I'm sure of, even then Murphy's law ( "Anything that can go wrong will go wrong".) sometimes intervenes. An ethical hunter minimizes the risks, knows his tools and his or hers limitations.
IMO getting your thinking right is more important than what tools you are using.