I'm ok defending the employees. Each of them did as they were told and trained to respond. I know that was a defense rejected at Nuremberg, but I think it's fair here.
But I have no defense for United. They failed to see that the steps they trained their employees to take could be seen by passengers and the public as hostile to customers under some circumstances. And when faced with a negative public response, they're still failing to see any blame rests with them.
I took root cause analysis training last summer. The CEO's letter suggests the root cause is the passenger's belligerence. But that isn't the root cause.