There is a fine line between legitimate grievances of customers and intolerable behaviour. Unfortunately, I feel that companies in service industries seem to take the opinion these days that any forceful complaint by a customer in person to one of their staff tends towards harrasment rather than legitimate feedback.
Take for example many posters we have around British railway stations with beaten-up staff photographed. While clearly unacceptable to resort to physical violence, the message it gives actually intimidates customers (combined with bolshie, unionised staff) - becoming don't hassle the staff with any complaints.
A lack of responsibility by the gate staff clearly caused this incident. Combined with a high probability that the staff there had no ability to know what actually caused the delay, combined to unacceptable behaviour, where the passengers had legitimate grievances.
Service industries require quality service - staff require the tools to provide this service.