Groan. Got into a convo recently about ethical play in board games. What it comes down to is that people don't actually understand what the word ethical means. My argument is that as long as you are both A) playing by the rules and
not motivated by an other factor outsie of winning the game, then you are always in the ethical right. What I mean is: don't cheat, and don't bring any meta factor into your play. If you are playing for second place, you are screwing up the game. If you are beating up on someone because they owe you $5, while knowlingliy passing up optimal moves, then you are messing up the game.
The opposition opinion was that certain moves make people feel bad, and that if you know they are expecting you to not play a certain way because of that, then it is unethical to do so. Unless you have turned this expectation into a house rule, I say these softies shouldn't be at the table.