I completely agree that the bottom line is whether the work justifies itself, but in this regard, I see no distinction between painting, photography, or any other two-dimensional medium. Whatever the medium, the frame must have some proportion. We may choose the proportion, or we may let someone else choose it for us.
I also don't care whether work is cropped or not, but knowledge of whether it is cropped will say something about what the work means and what the photographer's intentions were.
For those of us who work in static subjects, we do have the luxury of revisiting, reframing, reproportioning, rephotographing. For those who work in still life and the studio, arguably all compositions are fantasy compositions. In much of the nineteenth century, before the age of relatively high speed film, no photographic decisions were made in the fraction of a second.