On the side of impartial facts, I have to point out that cops (or security guards) don't need any particular reason to approach someone and initiate contact. And people are free to break off that contact until an officer has made an investigative detention (Terry stop), which requires a standard of reasonable suspicion...even then, they don't have to say or do anything unless there's a local law requiring, for example, displaying ID on demand to a police officer.
As a photographer and a guy who works in the security sector, I have to say that there are valid concerns about photography. The most effective way to deal with them effectively, however, is typically through [initially and hopefully remaining polite] non-threatening questions and evaluations of responses, not through imaginary bans and handcuffs.