g'day Dave, tough call
i think we should all draw our own line, and promise ourselves not to cross it
i have some doubts in regard to the article - the Smith example is a little tenous, Smith double printed a wood saw handle into an environmental portrait that already told the viewer the great humanitarian was involved in building a wooden structure, this 'manipulation' didn't change the meaning of the image, it just strengthened it's 'artfulness'
from my, perhaps limited, knowledge of the work of W. Eugene Smith, he did not 'overly' or regularly use manipulations as this article may infer
the example image shown - i doubt it is the same image manipulated, more likely a cut and paste job of several images taken at the same time, with the same content
question is, does the 'manipulation' change the meaning of the image?