Yes, I agree too. Now don't get me wrong - if I saw my absolute favorite musicians or actors, or someone whose work had affected me in a profound way, a few feet away from me, I would find it hard to look elsewhere. I would probably be speechless and would be staring quietly, from afar.
The celebrities don't want to be bothered. The thing is, if it were just one person asking them for a photo, or 2 people, it might not bother them. The trouble is, either folks get carried away and ask for entire photo sessions or 10 different autographs, or other people witness what is happening, notice there is a famous person in their presence and then they, too, have to have photos, and the crowds multiply. It ends up getting out of control.
Case in point - I live very close to The Grove/Farmers Market here in L.A., so I am there quite often. The Grove is well-known for being a good celebrity-watching spot in town. The TV show Extra films at The Grove most of the time. Maria Menounos, who is one of the hosts of Extra - as well as a current contestant on Dancing With the Stars - is there a lot, and she tries to escape to her dressing room or wherever in between segments.
In March I was at The Grove and I saw Maria. She had just finished shooting a segment for the show and she was suddenly surrounded by people, asking for photos. The poor girl could not get away. She was very polite and granted many pictures, but at some point she wanted to leave. She even told the photo-seekers that she was in pain (she had hurt her ribs a few days earlier) and that it hurt her to hug them, and yet everyone was asking her for hugs. People get excited. They get carried away. And then the celebrity can't escape.
I stood at a distance and took a photo of Maria with the zoom feature on the camera, when she was already graciously posing with/for another group. But I never would have approached her for a separate picture, and I never would have asked her to pose for anything when she was so clearly trying to leave.