I was sued in federal court for posting the photo of a man who had sued me for defamation. He sued me because I was causing negative publicity, but my statements were true/opinion and protected speech. I defended myself and prevailed.
I have also licensed photos I've taken of people for commercial use in advertisements. The law is not clear in all jurisdictions on the duty to obtain permission (CA and NY have statutes, some other states don't have a single case dealing with the issue). Also, permission is the duty of the publisher of an advertisement, not the photographer.
I photographed a parade many years ago, then a customer wanted to license a marching band photo for billboard use. The client correctly wanted a model release for a recognizable band member. I tracked down the school, then the student, got a release and paid the student. There would have been no way to get hundreds of releases when the parade occurred (and paid each person).
I just licensed a photo of an elementary school student for advertising use. I offered to get a model release, but the client was not interested. I am trying to locate the student anyway to pay her a modeling fee. The student is overseas in a developing country. I took the photo six years ago, but I know her first name, volunteered at her school, and donated a construction project. I can say from experience she will probably be happy the photo was used in this ad, and be thrilled to get paid. If I cancelled the deal out of concern she might object, she would probably be very disappointed and confused.
The above does not apply to "sensitive subjects" that the average person might be expected to object to being associated with (subjects like illness, teen pregnancy, abortion, smoking, criminal activity, etc).
As a footnote, my photo (when I was a child) was often used in advertisements. One had me appearing as a criminal. I was paid and liked seeing the ads.
That's my experience with this issue.