You have to understand that photography in itself is subjective. This means that photography does not show the objective and undeniable truth, even if you don't modify the photograph. For example, taking a picture from one angle or the other, selectively framing an image, taking one image and not another, showing someone 3 images of something and hiding 6 images of something else, etc... all this is editing. The only question is: where do you trace the line between "pure truth" and "fake image"? That is purely your decision.
Documentary photography deals with the "truthful" depiction of reality, and it's very important to depict something "as it is" in this domain. However, that is impossible, mathematically speaking. The only thing that's possible is trying to get as close as you can to what most people see as the "truth".
You can pretty much do ANYTHING in Photoshop today, so this feature won't really bring edited images to a new level of un-realness. However, it will make it easier to accomplish things that have been done for years before with hard work.
I think we should not be afraid of freedom. By freedom I mean that Photoshop allows us more and more freedom to create whatever image we like, regardless of reality. We have to be aware that images do not always depict reality, and if we know this, there is no problem. People have to go through this stage of understanding that images are no different than text: i.e. you can write anything you want, that doesn't mean it's real, and the same is starting to apply to images.