Mr. No Deer,
We are hunters that only shoot that which we intend to eat. Ethical (most emphatically) yes, from our viewpoint as subsistence hunters. Sporting, perhaps not; by the definition of others.
We rarely get the chance to shoot ducks but can equate it to hunting Grouse, if you will permit. Much prefer to shoot them on the ground as it allows far greater control of shot placement. As in, least amount of destruction to the breast meat (table fare). For instance, shooting from the back side of the bird allows the pellets to penetrate through the vitals with the least probability of penetrating through to the breast meat; with our prefered stalking method and shot charge.
I most strongly support the right of others to hunt as they choose, as the law may allow. Even then the law is not always right IMHO. As to what is ethical .... my limited experience indicates it varies with the times and group stating the opinion.
Best Wishes