The debate over whether or not image manipulation should be done and whether it is ethical or not rages on and in my opinion, much of it is unnecessary.
The opinions vary widely over disclosing what is real and what is not and some question whether any digital photograph can be believed. There are now even attempts to set ethical standards for digital photography manipulation.
Images have been manipulated since photography was invented and some of the most recognized photographers in history were heavy manipulators, like Ansel Adams among many others. You have probably already heard this argument. His and many others works are celebrated today as the Master’s of the medium.
Magazines, ad agencies, and other end-users routinely manipulate both stock and assignment photos. Most of the time the viewer never knows, unless a poor manipulation lands the image on the Photoshop errors sites. Rarely does anyone cry foul, unless of course the photographer did the poor job or cheated some rules.