Check out this Whitney Audioguide & Stieglitz's own journal entry about his famous work Steerage. It's immigrants leaving America to go to Germany, by the way.
Stieglitz found himself looking at the low-class deck called the steerage (full of immigrants):
"There were men and women and children on the lower deck of the steerage. I longed to escape from my surroundings and join them. Round straw hat, the funnel leaning left, the stairway leaning right, round shapes of iron machinery...I saw a picture of shapes, and underlying that, the feeling I had about life."
On second listen I'm not sure if he wants to be among the lower class or just is fascinated by their shapes, as an artist.