It is amazing how many people think the rules are made up just to cause trouble, or enforced out of spite. All the rules, even the seemingly nonsensical (like drinking your own duty free on board) are there for a reason, and should be enforced at all times. That people take offence at that suggests a level of egocentricity or paranoia. Bag size restrictions are partially to ensure the baggage will fit the stowage safely (ie not be a trip hazard under seats or put pressure on the locker doors potentially damaging the latches or hinges) and also to ensure their weight is low enough as to be unlikely to cause serious injury if they fall on a seated passenger. But so many won't consider the logic and will just rant and argue. There is a relationship between those with excessive baggage and bad behaviour towards crew, too. The reason is these individuals' selfishness. Personally, I'd support a policy of refusing travel outright to those with oversize cabin baggage as they're so often trouble makers.