As I have stated in other threads I believe photographing people in public is just fine, unless they specifically, beforehand, request not to be photographed and they are not intentionally being a "public spectacle". That to me is a question of common courtesy and mutual respect and falls under the same category as my napkin goes in my lap, I will not fart in church, open the door for ladies, etc.
Now someone said the photographer's occupation should not matter, for example a news photographer. I disagree. A photojournalist will photograph what makes him money, and only people who are "newsworthy" fit that bill. If you are just some joe schmoe walking down a public street, you are quite safe from them.
Next someone mentioned CCTV and security cameras. I also disagree with that analogy as I have accepted those on the basis that their images will only be used in connection with solving a crime or maintaining security, not placed in the public view which may happen with some random photographer.
Next, someone mentioned what we would have missed without the candid shots from Bresson, etc. I argue that a good outcome does not necessarily mean it was worth it to get there. For example, war has always massively advanced technology and helped society. In WW2 we gained nuclear energy, jet engines, advanced rocket propulsion, huge medical advances. Was it worth the millions of lives lost? This has been the conundrum through the ages back to the Roman Empire and beyond.
Is the end result, no matter how good, worth the cost, no matter how bad? That is a question each person will have to answer themselves, and live with that answer the rest of their lives.
Lastly, if you believe in a God, and that when everything is over you answer to them for everything you ever did, do you think when they ask you "why did you photograph this woman when she asked you not to", an answer of "because I could" will be very redeeming?
Allan