Re-pasting from an earlier post:
Would you ever resign?
Depends on a lot of factors.
i) The rating/strength of my opponent => usually indicates how competent his winning-a-won-game technique is.
ii) His time control situation vs. mine (Blitz vs. slow games? with a increment/delay?)
iii) If this is a tourney, how much of a rest-break do I get before the next game.
iv) The position on the board. This ties closely with i) as the margin of error in terms of "losing" positions can vary from "down a rook pawn" to "down an exchange" to down full pieces. If the margin of error that my opponent has is low enough (with respect to my assessment of his technique). then I'll play on.
For example, If I play a 1600-1800 player who is up an exchange (with no compensation to speak of) or a pawn (probably +1.0 to +1.8 on most computer's eval. scores?), while I am theoretically lost, I certainly don't trust his technique to be accurate enough to close out the game with lethal precision.
Chess games are won by cashing in on mistakes made.... Won games don't automatically win themselves! :)
Based on the above, I'd find no fault for my opponent not resigning for the same reasons.
At competitive play, there's always gamesmanship, ego and attitude and if you are training to play this game in a cool + calm + collected manner, you'll probably leave emotional baggage (irritation, annoyance etc.) at the door before you sit down.
It's just silly to let my opponent get to me using off-the-board tactics or feel arrogant/snarly that he dares defy the Gods of chess and not resign. That's a personality weakness that no amount of chess training will ever correct!
Update:
To add to your point about playing for a stalemate : Once you leave the little leagues (Class C, Class D, Class E) behind, you'll be crossing the line of sportsmanship/decency depending on the type of position.
Expecting a stalemate after a clever sacrificial combination = good
Expecting a stalemate when my opponent has Q+K vs. my K when he has more than 30 seconds on the clock => bad and you're probably not going to make friends with this guy anytime soon :)
In official USCF tournaments, is it bad sportmanship to not resign when you have obviously lost?
Online is different and irrelevent imo. And I know it's not against the rules.
I tend to be a play for stalemate player. I'm thinking about entering my first tournament, but I don't want to be displaying poor sportsmanship to my opponents. While it's easy to say, who cares, the answer is I do.
Just wondering, since I obviously don't know the atmosphere and expectations in otb tournaments.