Gymnastics, Photography and Paranoia

Yesterday I went to watch (and of course photograph) Abigail at her gymnastics class. The gym area had several signs up prohibiting entry to non-gymnasts, so I was photographing through the glass. Her instructor noticed me and invited me in. I sat down out of the way of the participants for a while, taking several shots. An officious lady arrived and informed me that photography in the gym area was prohibited. I protested. She insisted. This being private property, of of course had to comply. However, I cannot understand why officious people in so many places take action against photographers.