I don't think it's particularly rude either.. Do what you want, and let your opponent do the same. Why bring emotional baggage into it?
Maybe they don't know how to easily win with what they've got without putting themselves at risk for a stalemate. Maybe they could win quicker by promoting.. Maybe the just find some sense of satisfaction in an overwhelming victory.. Regardless, what has that to do with you? If you don't like it resign. Let them play the game the way they would like, and hopefully they'll let you do the same.. What more can you fairly hope for?
If they are in a helpless position some people play on just in case a blunder.so promoting would put them in a more helpless position and the game ends.
I HAVE SACRIFICED MY QUEEN FOR A PAWN PROMOTION.
Then I promoted into a queen and another and another.He finally resigned but in I personally think that if you let stay in the game the person will stay there and fight!!!!! YA YA YA YA YA YA YA YA