I was at a casual dinner a while back where a young man heaped his plate full of food and started to eat while the rest of us were waiting for the hostess to start.
The look on his face when he realized that he had unwittingly done something impolite was a mix of embarrassment, shame and surprise.
To me it was a perfect example of why etiquette still matters, no one wanted this young man to feel uncomfortable but because he didn't know basic etiquette he was now squirming in his seat not knowing how to act.
The biggest misconception about etiquette is that is full of fake silly rules. The whole point of etiquette is to give people a basic understanding on how to act that will make everyone feel respected and comfortable.