Since all Flight Attendants are trained the same way , they learn how to be polite to passengers, not to argue with them or create situations where the passengers can have the opportunity to escalate the situation and argue back and how to deal with unruly passengers.  The job of any Flight Attendant is not to get into any argument with any passengers, they  can make a simple request for a passenger to behave but it is not their job to plead their case to any passenger to get them under control, if a passenger is asked by a Flight Attendant to settle down and they ignore it the next step is to get the pilot and ground crew involved and they deal with the situation. And there are seldom if ever any Air Marshalls on a plane.  The point here is that the Flight Crew are trained professionals and they have a system in place for dealing with unruly passengers and if a passenger thinks different they are wrong.