The fare paid & service expectations can sometimes be poles apart. Whilst that, in itself, is no excuse for the behaviour that occurs, it can go some way to explaining how the $100 SYD return fare paid by the "ugg boot brigade" is the equivalent of the "Toorak tractor brigade" who've paid $800+ for JCL. It's still a big sum to them.
The frontline staff must have the support of their respective management in this area. If there is an abusive passenger, then there must be a unilateral approach to dealing with them. Void their ticket, involve the police, whatever. If the staff members are not supported, then this will continue, ad infinitum.