When you join a chess game, you have implicitly agreed on the time control. You have agreed that both yourself and your opponent will be subject to the same constraint, which is perhaps the greatest limitation on every game of chess. It would, of course, not make sense to join a game and then immediately add time to your opponent's clock at the beginning. If you wanted a longer game, then you should have chosen one. If you want a game where your opponent has a time advantage over you, that might be a different matter but advantages are taken care of by the Elo system so you could simply play against someone rated higher than you. So why on Earth would someone add time to their opponent's clock? There is good reason why the large majority of cases of this occur while the person who is adding the time is winning and while the time on their opponent's clock is about to run out. It is disingenous. It is not an act of kindness; it is a patronising act designed to make their win appear as though it had nothing to do with the time constraint when it had everything to do with the time constraint. It is done because they don't want to admit that their opponent lost on time rather than because they played well.
