I don't think any other art form has "died", or predicted to do so, as many times as photography has. When Eastman's Kodak first came out with their new roll-film camera in 1888, with the slogan "You press the button, we do the rest", it was though to be the end of photography. Anyone could take photographs without the knowledge to get the right exposure and developing their own negatives. Same thing happened when color film was introduced in 1935, and again when the digital cameras came into the market in the mid 90's. Today, we worry about phone photography being the degrading factory in art photography. Change always evokes criticism and worry. We are afraid to destroy delicate traditions and honorable legacies.
I think that is a wrong way to think about it. Instead of restricting it or trying to find the "right" or "pure" order to things, we should embrace all the qualities of our uniquely diverse medium. In only 200 years photography has evolved and changed exponentially. It has gone through a huge number of movements and styles in such a short amount of time, perhaps quicker than any other art form before it.
I believe it is impossible today to rigorously define or categorize the different forms of photography. There are too many variations, most of which are overlapping each other. Of course it is possible and in some cases useful to draw a line between different genres. Photojournalism being one of the most obvious since it has it's own ethics and principles. Photojournalism is based on the presumption that the picture portrays candid truth. No manipulation is allowed at the moment the picture is taken nor in the postproduction.
Truth has always played the role of divider in the realm of photography. In its origins, photographs were mainly used in educational purposes, to record and archive accurately what was. In other words, the truth. To make a photograph you always record something that physically exists in front of you so there always has to be some kind of a link between the image and the "real world". Whereas in painting, for example, the artist creates the art from her mind to the canvas: there is no need for any kind of a relationship to occur between a painting and the world that surrounds it. I think the unique kind of connection that photographs have with truth, is the reason why there has been, and still is, so passionate debates about whether image manipulation is acceptable or not.
One of the best known debates on photography's history was the debate between Pictorialism and Purism, specifically a series of articles written in 1930's between Ansel Adams, an iconic American landscape photographer and a devoted Purist, and William Mortensen, a groundbreaking Pictorialist.
Basically, they were attacking each other because of the differences in their views of what the essence of photography as a medium should be. Adams viewpoint is that photography should be about truth, from the negative to the finished print. Mortensen, on the other hand, used photographic manipulation to create his dreamlike images.