I think the reason motive is used to decide whether an act is ethical is because of this:
The consequences of an action can be the same whether or not the decision was ethical. For example, in the Eugene Register-Guard case we read about, Godbold said that he put the picture in there without really thinking. He knew it would cause a stir and that was about it.
He said that when people called in and asked why they placed the photos he said he didn't have an answer. Now if Godbold had actually thought about it and come up with a solid ethical justification for the placement, perhaps the readers would not have been as upset.
The picture would have caused emotional responses whether or not Godbold had strong reasoning for his decision. I think readers would have handled it better, though, knowing that he at least had a good reason for it.