The demise of courtesy

Should I stop teaching my children that when they are in a seat and an elderly person/pregnant woman/adult of any description comes along, they should remove their kiddie rears from the seat and allow said grown-up to take it instead? I mean, I seem to be the only person on the planet who still thinks this is a courtesy that should be extended. I walked into R.'s dance today and sat down in an unoccupied seat on one of the two small couches (the extent of the seating for parents who sit and wait for their child to come out of class). The woman next to me actually turned to me and asked me to move because her daughter (who was all of 7 years old) had been sitting there and gotten up to go to the bathroom. Are you kidding me? I'd have made my child remove him or herself if s/he was actually physically in the seat when an adult came in to wait but I had to move for a kid with a small bladder?! I bit my tongue because I think that making a snarky comment would have been as rude as her request but, really! Oh, and said child did come back, flop herself down, and remain in the seat as more adults came in who were forced to stand around waiting for a seat to open up or to sit on the floor until said child went into her class and left her seat. If you think this is curmudgeonly and old-fashioned of me to get myself into a lather about this, you are probably correct. But I want to know what is wrong with old-fashioned manners and courtesies? I am raising three children. Just imagine how obnoxious the world could be if none of us instilled courtesy in our children but instead taught them only to think of themselves first. Grumble, grumble, grumble.