You know, I wouldn't take legal advice from an open board on the internet if I was you! For the USA, Jimbob gave you the real answer. Although his profile says Australia, his answers are valid for the USA.
And before people from other countries jump up and down too much- laws are different in different countries!
Now ethics
is something else as you know and are wondering. I'll give you a question that I was taught as an undergraduate when it came to evaluating what people were doing with 'documentary' photography, which your situation at least bumps against-
Who is getting more form this photograph, the photographer or the subject?
Photography is full of cases where someone goes into a community, a place, etc., takes the photos, turns them into a series of striking prints. And sometimes the images make the subjects' lives better.
Look at Eugene Smith and Minamata, where he not only took some amazing photographs but used them as part of a campaign to get the mercury poisoning stopped and victims compensated.
Then look at Gary Winogrand and how he thrived on making people look stupid. But it got him grants and teaching gigs and gallery sales.
My own ethical standard for showing images taken in public or quasi-public is whether I was the person shown, would I feel as if my life, my being, had been cheapened or lessened? And in showing the image, am I saying anything about people, the person shown, that is worth saying?
--
Dan Daniel
http://dandaniel.zenfolio.com/ 
The fun was just getting going.... 
