A topic that has been discussed countless times.
As far as I'm concerned, I always resign because when I'm down a lot I know that I can only recover thanks to a resounding blunder by the opponent, and this makes me lose interest. However, it doesn't shock me or bother me at all if the losing opponent keeps playing until he gets the checkmate. That's his business. It's a game, and he can live it as he pleases. Seriously, frivolously, as a simulation of a war, as a sport, as a pastime, or whatever he wants, depending on how he sees the game of chess.
Everyone has their own motivations when they play chess. What matters is to play fairly, and not to cheat. I would add, it would be nice to acknowledge the defeat by congratulating the opponent, at least formally, as a courteous gesture at the end of the game ( which, according to the rules, ends with the checkmate ). Otherwise, a chess move is just a chess move, nothing more. Personally, I don't attach any additional meaning to what one does on the chessboard with his pieces.
Btw, I never tell nor ask for resign. Instead, I do compose a mask of indifference and wait patiently for the unavoidable win.
(if it's a child, I don't mind: childish behaviour do belong to children).