I was very rarely asked. Passengers were probably afraid of breaking the camera. It was a situational thing. I wasn't nuts about it but often consented, especially when kids were involved, or when the passenger was somebody that I had met before & developed a professional relationship with. This also happened with first-time riders, and I always liked to accommodate them as much as possible. I was always afraid that there would be something wrong with my image & the picture might reflect Amtrak in a poor light. When you're busy working, you don't always realize your hair is mussed up, for example. I was never really worried about stalkers, but I can understand that some OBS employees --- especially women --- might have that concern.
Bottom line: it's an individual thing, and it's situational.
Tom