Most of the accidents I have witnessed have been minor, with one exception, which put me off airshows forever. In the early '80's several of us flew to Oshkosh for a day. A Siai Marchetti pilot was demonstrating an SF260. The announcer said that the pilot would now demonstrate a spin. He did. The problem was that he was only a few hundred feet up. He entered, got the rotation stopped, pulled up, and slammed into the runway right in front of me, going down fast in a level attitude. He killed himself. The flying stopped for the day, and it was hours before the runway was cleared at the end of the day so we could fly home. What a waste.
In my capacity as a volunteer firefighter, I've had to attend many crashes in our area. I've had to help lift two dead friends out of their crashed planes over the years - you can't not, they're your friends.....
It reminds you to fly well though...