...The question of whether Dorothea Lange was taking these pictures 'for her own self gain' arises, I suppose. She was being paid by the Farm Security Administration for the job (and indeed directed quite closely about what to take pictures of).
I think there's a big difference between someone who has put years into a career as a documentary photographer/photojournalist/professional being commissioned to record and a casual snap of a random homeless person. I think Dorethea Lange actually took photographs with great empathy for the people she was photographing.
Most of the people on the streets here don't mind having their picture taken - many are quite extrovert characters, but they do expect €1 for the pleasure.
In some respects I suppose taking photographs before asking permission is the only way to get a true representation. Once asked people will pose, or just the fact that they're aware that they're being photographed will change the way they behave.
To my mind there are plenty of valid reasons for recording all walks of life and the whole of society. It's just the attitude of the telephoto snapper who's to fucking scared to actually talk to anyone that really annoys me.
BTW: Apparently there are some B&W photographs of me on a FlickR set looking as much like a homeless bum as anyone else in Granada

No idea who took them. No doubt I had a bottle of booze close by also!
e2a; Ha ha! Found it and fuck it's a bad photograph. Nice shiney baldy head. I'm going to sue the fucker for mis-representation. Early morning in Bib-Rambla in winter. Freshly shaven head
I've just found lots of shots of mates also. This is a laugh.