There are honest mistakes and then there are careless mistakes. It is the careless mistakes on the green slopes that drive me crazy.
Net net, people should ski slowly in slow zones if it is crowded. And on green trails, everyone should be cognizant that there are going to be "green" skiers on the trails, including little kids who can get really hurt if anyone over 100 lbs runs into them at speed.
That said, I've made stupid/careless mistakes. Last month, on lower Cloud where the entrance to Santanoni is, the girls were stopped on skier's left waiting for me -- I had stopped a few yard behind them on skier's right to let them pass so I could follow them down. I then skied across the trail -- from a dead stop, right to left -- without even looking. A guy trying to maintain speed for the traverse to the Saddle had to veer to avoid me, and ended up threading me and the girls. Because of me, he almost took out all three girls going what was likely over 30 miles an hour. All three would have been in the hospital.
At the time, I was steaming. But in retrospect, it was my carelessness -- brought about by a relatively empty mountain -- for not looking behind me before crossing the trail.