Sometimes, rarely, the complaint might involve a particular employee. In any group with that many people you will inevitably run into an occaisional turkey. And even if the employee in question is not in fact a bona fide "turkey" -- well, we've all had our bad days.
Instead, most of the problems are with the actual airline itself, either because or their cavalier attitude to contract law and obligation (i.e. the airline has no obligations whatsoever, yet the passengers obligations are absolute) or the complexity (some would say insanity) of their own rules, or the incessant rule changes that are not properly promulgated, and so on. In this case the airline itself, and only the airline, is to blame.
Even when the root cause is beyond the airline's control (i.e. whether) the airline is often at fault in compounding the problems. The lack of information and the overwhelming amount of (unintentionally) inaccurate information just makes things worse. And as someone else noted most passengers don't feel that the airline is trying to help them, they just feel completely abandoned. (Last December when I was stuck in YYC overnight because of snow in YVR and YYC even I felt exhausted. So if a certified/certifiable "road warrior" can be overwhelmed by that situation with the airline, then what is expected of your once-a-year flyer?)
It doesn't help that somewhere in the fine print at the bottom of the back page of some mythical tarriff it states that the airline is not responsible for weather delays. What it needs to say, in big, bold letters on the front of the ticket, boarding pass, baggage receipt and on the side of the plane in 1m high letters is "If there's a problem with weather, you're on your own!"
Strange as it might seem, I think most people would initially be surprised when they read it, but would quickly accept (and understand) it. And when the weather comes in, they'll be prepared for the Kafka-esque world they'll find themselves in. More importantly, they won't be complaining about or to the airline.
In this case, and others, it's all about managing the customer's expectations.
{still more to come}