Interesting thread and I think the worse thing about it is the choice or words in the title. I do not see this as having anything to do with ethics (unless you try to cheat, fraud or break laws etc) and more to do with where the boundaries between art, digital art and photography lie.
I agree with those that say that as soon as you add elements (or take away elements) from a photograph then you are entering the world of make believe, and consequently art. You are creating something that did not exist, but that your mind wanted to see.
One example of this, would be the CR forum member Gary Samples who posted a picture of two eagles fighting. The one on top was pushing the other into a stream. It is an amazing picture, and I would bet money on the fact that Gary changed very, very little and most definitely did not add or subtract anything from the shot (which is in the 1D X image gallery section. I suggested at the time that he enter it into a competition as I had never seen anything like it. That is photography. If he had added a fish to the beak of one and possible added a bear in the background then it becomes digital art. Incidentally if someone were to paint that moment on canvas, I am sure it would make for an amazing painting too. That would be art.
HDR is on the very verge of this, and possibly on the verge of video too, but as it does not actually add, or subtract, elements that did not exist I still see it as photography.
I am quite possibly the worse artist in the world, and that is saying something considering some of the c**p that sells for millions. The camera allows me, and possibly many of us here to be better artists. We recognise the beauty of something, but if you give us paint, canvas and a brush, then it just is not going to come out the way we would like. I admire anyone like Banksie (is that the right spelling?) and I adore his art. I make the best of my limited talents and try to capture moments with a tool which allows me to do so, but I am a billion miles away from ever being an artist. Even digital art is absolutely amazing and requires some very special people to create what they do. Me, I just point and shoot.