On messages and society

The following is a conversation that took place today between me and my mother. Names have been changed to protect the innocent and the not-so-innocent; phrases have been changed because I've clean forgotten 'em and I need to paraphrase. I am well aware how rude I sound and how reasonable she does; I am also well aware that those are also sounds, as opposed to content - and what I say may put me in the right. It's up to you to judge.

Mum: Oh, at school tomorrow, will you give Dan [my friend] this card? It's for Jenny's birthday. [Jenny is Dan's mother and Mum's friend; her birthday was a few days ago. My mum can't be bothered to find out her address, instead relying on me and Dan to exchange things.]
Me: No. I'm not your messenger.
Mum: But she was very upset when I promised Dan would get some chocolates and the card would be late. [As well you know, it was my birthday a little over a week ago. My mum put some chocolates in my schoolbag to give to people, despite me explicitly saying I wouldn't give them out - I would forget, I wouldn't have time, I'm not into that kind of thing - I have my reasons. Of course, the joyous day came around, my mum put the chocolates in even though I said not to, I forgot to give the chocolates out, and my mum tutted and pursed her lips but I thought the matter was forgotten. I didn't count on my mum playing the politeness game.]
Me: I'm not your messenger girl and Dan is not your messenger boy. If you want to give her the card, I can ask Dan for his address.
Mum: Humph. [Here she turned around, having been rather offended by my grievous comment, and sniffed in the dignified manner well-befitting of such a noble and imperious woman.]

Being the naive idiot I am, I assumed the matter forgotten, as I do when people don't talk about it. But lo! as I was trying to do my chemistry homework she came in, held erect by wrath. (Putting aside the purple prose for a moment, which is supposed to be quite snarky - but take it as you will - she was actually pursing her lips and looked like she'd been sucking lemons even more than usual. Just saying.) And with her coming I still didn't understand that she wanted to bring the matter up again. It was only when she started blabbering in my ear while I was writing that I finally understood.
Thus the interlude came to an end and I wrote more dialogue.

Mum: Will you take the card tomorrow to give to Dan?
Me: I've already said no! I'm not your messenger girl!
Mum: How come when Dan and Susan send you cards it's OK but when I try to send a card it isn't?
Me: Because I have nothing to do with the business between you and Jenny and Dan has nothing to do with the business between you and Jenny. We are not your messengers!
Mum: Well, I'll tear this card up and explain to Jenny why. I'm not going to send her a card weeks late!
Me: Fine, I'll tear it up!

In actual fact it proved quite hard to tear up, even trying to take it out of the envelope, and I handed it back without having so much as dented it. She took it and went out of my room (finally...thank God...), and I finished my chemistry homework. And all was good, until they made a sequel.

Is there a moral to this story? Is there a motive? Is there a plot? All these questions and many more remain unanswered, but I still have a couple of things to say:

I stand by my comment about the messengers. If you want to give someone a message or gift, give it to them yourself, or mail it, or get someone else to give it directly to that person. Do not give it to somebody, who will pass it on to somebody else, who will mail it on to a secret address in Timbuktu where the gift will be scanned and securely sealed before being transported overseas to South America and then flown in a private plane to the person with roses and lavender. True, it is polite to give cards and gifts promptly, but it is not polite - at least not according to me - to rope in other, unrelated people to do it for you and assume that they will because they're acquaintances or blood relations. (This may not be a breach of etiquette, but I haven't consulted a manual, so I wouldn't know. However, it is most certainly a breach of morality, as it is wrong to use other people as workhorses so you can ingratiate yourself with someone.) Similarly, politeness is not like a pair of scales. It does not involve measuring gifts and thank-you notes against each other and doing whatever it takes to make the scales even. Yes, it does involve give-and-take, I won't dispute that, but I will dispute - and readily - the assertion that returning favours comes above all other social and moral graces, including pushing neutral parties around to do your bidding. Yes, it might make some marvel at your social niceties, but it will make others recoil at your lack of moral grace and your utter pushiness and pettiness.