Someone once told me that good manners are the oil which lubricate the engine of society. I'm not sure who, it might well have been my mother, although it doesn't sound like one of her metaphors.
Yes, they are rituals, and yes, many of them are, on the suface, pointless. However, they serve a dual purpose.
Firstly, as Wharfinger says, etiquette and good manners prove that we have taken the trouble to learn the rules and conventions that will avoid offending people. And that does show respect and consideration for others. It's the acquisition and application of the rules that are important, not what those rules are -- after all, why in chess does the knight move the way it does? It is pointless -- but it's the rules, and if you don't know them, nobody will want to play chess with you.
The second purpose is more subtle. Good manners allow you to interact with people you would rather not spend time with, but who you are forced by circumstances to encounter. The hideous screeching woman one of your best friends has fallen for, your boss' pompous husband, your irritating young cousin. Manners and etiquette provide you with phrases to speak, and constraints to prevent you from saying what you might like to, preserving harmony and avoiding conflict, in situations where any such conflict might be damaging -- to relationships with friends, your family, to your career, whatever, and where being open and honest will have no long term benefits. After all, you may never have to see the person you dislike again, or only occasionally, and for short periods, so what do you gain from voicing your dislike? The polite conventions give you something to say, so you don't cause offence by ignoring someone, but don't lead you into conversations of substance where your feelings about the other person become apparent.
The point of ettiquette isn't the superficial actions you undertake, it's the deeper significance of the fact that these actions exist to help everything run smoothly