I am mostly a sports photographer but I have shot weddings on multiple occasions. I have refused to relinquish the rights to my photos not because I wanted to make more money but because I didn't want my name tarnished by some schmuck who bought the rights to their photos and then did some awful editing to them and uploaded them to facebook and said "taken by xxx photographer" (me). That is the worst fear of any photographer. When I take a photo I usually know at the time of the shutter press how I am going to process that photo and what part of the story that photo is going to tell. However if I give somebody else the full rights of that photo to do whatever they want and yet still give me credit for physically taking the photo, my name could be unintentionally slandered by the editing offender who did a terrible job at the editing. I always keep the rights to my intellectual property to protect me and my livelihood so I can continue doing what I do.
As Mundus Vult has mentioned many times in this thread, "The rationale behind this actually makes sense (assuming we want artist to make art)." Personally, I could probably not continue to do what I do if everybody out there had the right to edit my photos however they wanted. Some perspective client out there would see a photo that I took (and the credit was given to me) but it was edited by some random guy and did a terrible job, the perspective client might look elsewhere to a different photographer. Granted, if I did everything myself and I still did a terrible job myself, well, that's on me and that is how the herd is thinned -so to speak. But I just don't want to me "thinned" by somebody outside of my control, if that makes sense.
Mundus Vult has done a very good job here explaining the reasoning behind the copyright laws we have today regarding photography. It all stems down to protecting the artist (producer) to ensure the artist will continue to create art. If all the artist's work could be freely manipulated by other people, what would be the artist's motivation to create additional works?
Copyright law pertaining to intellectual property is similar to patent law. (Putting aside some of the patent abuse some companies have figured out how to do), patents were originally created in America in order to PROMOTE invention and advancement in society. If some random guy could "rip-off" the original inventor of something, the inventor probably would not have had the motivation to create it in the first place knowing it could be "stolen".