It's when you start adding elements not in the original capture, It's no longer photography.
I could not agree more, adding to the image changes it to photographic art; however, subtracting (the corner of a building, a flying bird, contrails, et cetera) is perfectly acceptable. Obviously anything you can do it a wet darkroom, you can 'legally' do the same in photoshop.
On the off-chance your comments aren't tongue-in-cheek, what's the (relevant) difference between adding a flying bird and subtracting a flying bird? (They're both additions anyway.) And why is it obvious that the ethics of all of this are defined by what can be done in a wet darkroom?