In a recent magazine interview, Mila Kunis shared her views on photoshopping. She put it this way: it's like if somebody wanted her name, but they didn't want what she really looked like.
I think this is the best argument against photoshopping I've heard so far (not that there aren't many other good arguments).
I hope the industry listens. But if they don't (as likely), I suggest that celebrities start insisting that their names should not be used on photos that have been edited to not look like them, because that would be false advertising. Why would they want to do that, you may ask. Well, I believe the first few celebrities to start insisting on this would gain loads of public respect, and the rest would just have to follow, thereby ending this unhealthy culture of photoshopping.