We know very well that when a journalist reports a story he does so with a bias. He will leave things out he considers unimportant, he will emphasise things he considers important.
Why do we impart this particular purity to photographic images?
There's no purity. A friend showed me a news video shot in his hometown in which the reported says "I'm in downtown Sherman and this is about all there is to downtown" with nothing behind him but a house. My friend pointed out that just to the left is the IGA grocery store. That's misleading, primarily in the words he stated alongside the image, but it still shows something that really exists and I can look at it and enjoy it more knowing that it's showing me a place on this planet that really exists at this time. Purity is a fool's errand. But an image with stuff arbitrarily added or removed by the photographer is just something I have no interest in looking at. We should expect that photojournalists don't create scenes that don't reflect what was in front of the lens. We see differently than the sensor sees, so there's leeway and I won't get into how HDR can be used to change the mood of a shot, but certainly adding or removing objects from the image changes the physical reality. Outside of photojournalism, it's up to us to determine what kind of manipulation matters to us and then figure out who's doing photography we want to look at.
It will be a sad day for photography when this becomes the norm, because IMO, most photographs just aren't that good if you remove the connection to the real world. Most of the images we hold up as classics would be forgettable illustrations if, for all we know, they were created in Photoshop.
How about
this? Heavily processed. No removing or adding things, true. But all distorted to show something else than what was in front of the camera.
I'm far from a purist. Those are all mild edits. Any two people will see a scene differently; different cameras, films, sensors, lenses see it differently, paper portrays a fraction of the range of brightness that was present. Reality is a fool's errand. But we can look at a picture of a man stepping into a puddle and the success of that photo depends wholely on that fact. The cropping helps the composition, but turn that water into a highly reflective tile and you might end up with virtually the same composition (same reflections) but a very different picture. We appreciate this photo because of the moment in time it captures, not because it presents a 2-dimensional collection of shapes in shades of gray. If we were to learn that it was faked
How about objects that were removed from the frame by choosing a particular view? How do you know that there isn't a dead cat lying just outside of the frame?
I don't care - or, rather, I get to wonder what might be just outside the frame. I don't mind that both realities exist

It doesn't bother me that I don't get the whole story, or that I might even be fooled into the wrong story. That's part of the power of photography; it's ability to show us a selective view of the world at a moment of time. It's kind of like the difference between not being told the whole truth and being lied to. Think of a movie where you're surprised by a twist at the end. If it's a really well done movie, with an intelligent plot, and the clues were there if you go back and look for them, you love it. If it's really contrived, you aren't so satisfied. And if the writer had to purposely deceive you along the way to surprise you, you feel ripped off.
And is reframing to create a certain impression really that different from removing something after the fact?
It is for those of us whose appreciation of photographs is based on their connection to the real world. I'm not normally a fan of abstracts, but I picked up a book called "Color Correction" by Ernst Haas a couple years ago, and there are many abstracts in it that I like a lot, due to a combination of a fascinating composition and trying to puzzle together just what, exactly was in front of the camera. If these were by a recent photographer and I were to learn that they were created by layers in photoshop, that wonder would be gone.
Like I said, I'm far from a purist. I like Mark Tucker's portraits in which he uses textured backgrounds based on other objects he's photographed in the past. It's obvious and I can look at the images with that knowledge in mind and appreciate them with that context.
I am not saying right or wrong - but I do wonder where that purity aspect really does come from?
It's not purity so much as a connection to the real world adding to my appreciation of the photo.