I read a story about the woman who was arrested. It said that it was announced to hold all cheering to the end. It does make the ceremony ridiculously long, and then people can't hear their child's name being called. My graduation was held at a large open-air auditorium (popular concert venue) and I remember we were told no cheering, calling out, clapping, etc., for each person going across the stage. It was supposed to be a dignified, important ceremony. Then, at the end, enormous cheers went up and we all threw our hats in the air. To me, that shows the respect and dignity of a ceremony like a graduation, and then the joyfulness at the end. I would find it appalling if, after each name was called, parents were shouting "That's my boy!" "You Go Girl!" "Woooooo!" - especially when specifically told not to. I would have been mortified if it happened to me.
There is a time and place for everything. The jumping up and down & screaming with joy is at the END, NOT when they are supposed to solemnly walk across the stage & receive their diploma. THAT is supposed to be dignified. I've been to graduations at my high school for myself, friends in other grades, and my older sister. My younger sister - at a different high school. My brothers' for college. People never called out and cheered and clapped for their individual kid.