Is it ethical to flag an opponent if you are down bad?

Running out of time is part of the game. If you want more time, there are daily games.

In classical it's not so much that it's illegal as that it's effectively impossible. Nearly every classical tournament will feature a thirty-second increment. If I have a decent endgame advantage, then 30 seconds a move should always be enough for me to at least avoid losing. (If it's a complicated, double-edged middlegame, then it wouldn't, but that's not what's meant by "dirty-flagging").

In the days before increment, it's true that there were rules designed to protect against dirty-flagging. If I'm remembering correctly, the USCF rule was that if you were low on time in a position in which a class C player would have a 90% chance of managing at least a draw against a master (given adequate time), then you could claim a draw. Obviously, this led to some difficult judgment calls, and lots of tournament directors found themselves enduring the ire of one player or the other, so as soon as digital clocks became widely available, this rule was ditched, to the considerable relief of anyone whose job was to run a tournament.

Flagging in chess—winning a game on time when you’re in a losing position—is a tricky topic, but generally, it’s considered part of the game.

My opinion.

If it doesn't go against the rules, it's neither ethical nor unethical, it's just legitimate. Furthermore, in blitz and rapid games ( you lose due to time even in the latter, it happens to me very often ), time is part of the game, so it must be considered a resource. If you are winning but have very little time left, you are probably winning because you have used a lot more time to think, and now your opponent is turning it against you. It's the game.

If you play blitz or rapid, you accept the various side aspects. Using flagging or not is at most a matter of "style", I think.

I'm not a chess expert. But, it seems to me if chess very loosely models combat/war, then "running out the clock" (e.g. seasons/weather) to the opponent's expense seems reasonable and should be expected by all sides.

As for a question of "ethics", I would defer to rules. From what I'm reading, there is no rule against "flagging".

Frustrating, for sure.

At my low level, flagging is less of a concern than just trying to avoid blunders <grin>.

It's part of the game!