Allow me to interject alittle here on the issue of photography and social etiquette..
The relationship between the photographer and his subject is indeed one that raises many questions. Street photography, regardless of motive, is at the base level exploitative at the very least. The end product, the photograph, is an interesting portrayal of social dynamics, but it is also on many levels open for interpretation. I believe the main problem here in understanding the concept of 'social etiquette' in photography lies in the problem of objectivity, or rather, the perceived concept of objectivity and the presumption that there is a social, concrete example of what objectivity entails.
Photographers, or anyone for that matter, have to realize that the facade of objectivity is an amalgamation of half-truths, personal subjectivity and biases, encased and protected in a facade of 'objective' social rules, hence realizable and thus ultimately concrete and unassailable in nature. Bourdieu has written extensively on photography and once argued that, 'Only a naive realism sees the photographic representation of reality as realistic; if it appears objective, it is because the rules defining its social use conform to the social defintion of objectivity. Herein lies the paradox of the camera because it can both obscure and reveal, both at once, revealing a fundamental conundrum in our logic because we assume that what the camera reveals is true because we can see it.
What i'm trying to say here is that the camera and the photograph it produces can never be objective in nature. Insofar that one views photography, especially street photography, as exploitative in nature, it is because one is forced to act within the rigours of a social contract that informs the individual that there is an empirical truth, a formulae if you may, to how people must conduct themselves.