We all certainly have a right to ask that our photo not be taken, in or out of public. How a photographer responds to that request is an individual choice that may or may not rise to the level of an ethics issue.
What many seem to assume, however, is that a bubble of legal privacy surrounds us while in a public space, making any photograph a privacy violation and requiring prior approval.
That's not true, of course, but judging from the anecdotal evidence posted at RFF, enough people believe it to fuel commonplace unfair and aggressive confrontations with photographers, or worse.
i think the proper response is to assert and defend our rights to take pictures. That does not mean being abusive towards someone who is abusing you. It does not mean trying to teach someone a lesson. That will only make someone who is already upset even angrier, and will not change their behavior.
Instead, raise the issue with the people who determine policy. For example, if a mall cop hassles you while parents are happily grabbing phone and p&s shots of their little cuties, don't expect the mall cop to care one way or the other. Even if he did, there's nothing he can do about it. Go to mall management. They might simply alter policy to permit p&s and phone cameras while banning DSLR's, but c'est la vie.
If you are shooting in a public space and someone asks you to stop, saying photography is not allowed, ask them to explain why their facility is exempt from the general understanding that photography in a public space is always permitted. if you disagree, again, go to management. In almost every situation, the people who tell you to stop did not, and cannot, set policy.
If someone, in private or in public, asks you to avoid taking their photo, then each of us needs to decide for ourselves how polite we want to be.
