Meryl Arbing , Oct 08, 2005; 08:50 p.m.
Those cultures that retain a belief in 'sympathetic' magic (where something that was a part of the person, like nail clippings, hair, blood or even an article of clothing) could be used to cast a spell or curse. A part of the 'victim' is essential in creating a 'voodoo doll'.
The 'voodoo' doll is an 'image' of the person and it isn't a far stretch for superstitious people to view a photographic image as having similar 'power' and be afraid.
I think you are correct. It is good manners (and in some situations good sense) not to take pictures of people who object.