If you talk to the average people on the street about video/phone/internet surveillance, you end up in a never-ending round of the same arguments pretty quickly. Here is a way I came up with during the ChaosDocks to get out of some of these situations:
If someone comes up with this argument, ask him to follow you to a non-public room (a waiting room will do, it just needs to be off the street in order to eliminate legality arguments). In that room, take out a camera and ask the person to get naked so you can take some pictures.
If the person refuses to get naked, which he or she most likely will, ask the person, «Do you still think you have nothing to hide?»
If the person does get naked, he or she is either hitting on you or beyond good and evil. In the latter case, no debate is possible, in the former, none may be required. In fact, this hitting on you might even be something the person might be willing to hide from his or her significant other. Otherwise you at least get some interesting photos.
Amendment: Also, I found this: