The people who "insist" that a photograph "must be sharp" are really little more than button-pushers who view photography as a purely mechanical activity, devoid of artistic expression.
THAT is the point of view that spawned pictorialism. Pictorialism was a response to the flood of amateur snap-shooters who worked with basically, no artistic interpretation, but instead just pointed their cameras and used them as mechanical recording devices. People who wanted nothing more than sharp, clear photos depicting EXACTLY WHAT they had seen, in real-life.
The idea that successful photographs must be super-sharp, and clear in order to be good photos is a point of view still alive today in the minds of many people, almost all who have never studied what photography truly can be, when it is practiced for the sake of art, self-expression, or exploration of ideas. Of course, if one's idea of photographic greatness is shooting the same basic pictures of men and women dressed up in almost identical costumes, week after week, in the 15 or 20 same locations and rooms, for years on end, then sharpness of the results is probably going to be considered the critical determining factor in evaluation one's success as a photographer. Well, that,and whether the client's check clears.
Those who argue that photography "must be this" or "must be that" in order to be successful have a very narrow-minded, simple concept of photography. The idea that "sharpness" is an absolute necessity for successful photographs is a joke. It's an incredibly lame, simpleton's argument. People who advocate that images must be sharp, and must be representational or accurate images of what existed in reality are not artists. Just button-pushers, who view photography as purely a mechanical recording process, devoid of any artistic potential, but really good at direct and pure recording of scenes and people.