I'm not commenting on the sarcastic reaction but on the specific notion that saying thank you is not necessary when being the recipient of a favour one did not ask for.

For me the starting point is that politeness is not "compulsory" but something you put into practice to be nice to others, show that you do not believe your rights and comforts to be more legitimate than theirs, and showing some form of empathy towards others.

Based on all of that, to me, the fact that you did or did not ask for something has no bearing at all on whether I would wish to be polite to someone who does something nice for me. It does not matter that the Christmas present from aunt Beth is horrid and the last thing I'd want, I won't say thank you based on my having asked for it but based on my understanding that she offered me a present to be nice to me and try to make me happier/more comfortable/etc .Exactly the same goes for the door. It is irrelevant (to me) that I do or do not like having the door held for me, if I think that the person did it to be nice and thinking that it would please me, then by my book, I would thank them to be polite and show that I appreciate the gesture.

In a way, I find basing politeness on whether or not something pleases me almost at odds with my own criteria - it would make politeness something very transactional, almost self-centred, whilst to me its basis should be empathetic. To be honest, I even say thank you when people stop at the pedestrian crossing to let me cross. I know they have to, but I still think it's decent of them so hopefully an extra thank you will just make their day ever so slightly more pleasant.

I do agree with your other point that I am not glorifying former educational principles at all costs. I do however resent the fact that nowadays everyone is treading on eggs for fear of imposing ,contradicting, or offending others. Some of my friends raise their children with an explicit principle that the kids should not be obliged, contradicted, or frustrated, that they should effectively do what they want. I find that attitude unhelpful to the children and irresponsible. Ultimately, much of life is about being contradicted and frustrated by others, sometimes unpleasantly or unfairly. I do not think that maintaining a myth that no such contradiction or frustration is there or ever legitimate helps anyone. I also think that empathy (ie trying to view a situation from the point of view of the other person and not just from your own) is absolutely critical and something that must be educationally encouraged from the very beginning. From that point of view, I think that when parents see their child put his feet on someone else's suitcase, it is not unreasonable for them to ask him to stop and explain that he would not like someone else stepping on his things. To me, that lesson would have actually been more valuable to the child coming from the parents (because it would have been on the basis of empathy) than from me (because by nature, I was an interested party so it may sound that I too was merely defending my own selfish interest). Similarly, when I was a kid and taking the bus from school every day, if kids stay sat when an older person came in, the bus driver would have no hesitation to tell them to stand up as an older person had more need for a seat than them. Again, I think that it is a valuable lesson to teach and that parents who do not deliver it to their children are not only being unhelpful to them and unfair to others but are also under-evaluating their own children as in my experience, most kids are perfectly capable to not only understand but even genuinely embrace such logic if you point it out to them.