You don’t harm people by making their photo
Let us consider the physical fact of making a photo.
You lift up a little metal box, and you press a button. That’s it. What is so offensive about the action motion and act of making a photograph? Nothing.
Yet of course, people are more offended that somehow that you are “taking” or “stealing” their soul or image by using a photo capture device. And if we think about the physics, who owns the photons that bounces off their bodies?
Anyways, you’re not harming anybody by making photos of them. You’re not physically touching anyone when you take their photo. The only perhaps aggressive thing that can “harm” someone else is shooting with a flash at full power at night, when the harshness and brightness of the flash can cause visual pain to the eyeballs of your subjects. But otherwise, taking a photo of someone without their permission does them no physical harm.
Why do your subjects get upset or offended?
I’ve noticed that sometimes people get angry if you take their photo, if that individual has something to hide.
For example, let’s say you make a photograph of a nice coupe in the streets (a man and a woman). But what if the man is cheating on his wife with this woman? You’ve just captured “evidence” that he’s cheating on his wife. Thus, the man might get aggressive and threaten you, and try to get you to delete the photograph, because he (of course) doesn’t what the “proof” that he is cheating on his wife to somehow exist in the world.
Also sometimes when I photograph certain marketplaces, people don’t like to be photographed because what they are doing is illegal (like selling puppies, birds, etc). Or sometimes some people are illegal immigrants, and they are just afraid that you might be some undercover immigration officer or something.