that doesn't work because you can't define "the problem". creating a long list of cases where photography should be allowed and where it shouldn't would require the photographed person to prove that their photo falls into the cases that are a problem. that puts to much burden on them, and makes it more difficult to protect themselves.

each person has a different feeling in how they are comfortable with having their pictures published. therefore the only sane thing to do is to give each individual the right to control that.

it's like copyright. by default all rights are reserved, but i can give permission to copy if i wish.