Is it bad sportsmanship to keep playing when you have NO chance of winning?

Why do people keep playing on and on when they can't win? Just resign the damn game. It's a waste of your time and mine. 

Am I right? 

Chess is a waste of time to begin with. I cannot fathom why some people can play 10mins+ of chess. Chess is so easy. All you have to do is checkmate the other king and since it's a game of PERFECT information, everything is known... Since  it's probably a draw for two great players anyway, why not just agree to a draw and then go watch TV or something?

Different people feel differently about resigning.

We've had people post outraged complaints about opponents "resigning like cowards" instead of playing out to checkmate.

Sometimes you can draw...

I dont ever resign

One of the famous axioms of chess is "no one ever won a chess game be resigning," that said I certainly understand your point. My pet peeve is a player that is really behind and at some point simply stops playing and let his\her time run out.

Trying to apply some intangible 'sportsmanship' tag on top of the ruleset is never going to end well.   
The rules are what matter, because they can be enforced.  Some, many of the rules overlap sportsmanship -- eg if you are abusive and get reported.   Playing to the bitter end is allowed. 

Online I won lots of games beeing a full queen down, mostly bullet of course. Opponents were higher rated than you are...

@Kevin_Grem. Agreed. I'm not bothered about time tbc. Let's just set em up and play again. You've got some salty people out there but losing is a part of growth. A draw?? Lol.

Grandmaster Matulovic of (then) Yugoslavia was infamous for refusing to resign, even in utterly hopeless positions.

According to David Levy and Radojcic,

- Matulović was involved with controversial incidents. Over the board he played on in hopeless positions when grandmaster etiquette called for a resignation, allegedly in the hopes of reaching adjournment (suspension of a game for resumption on a later day, common in tournament play at the time) so that the news reports would read "Matulović's game is adjourned" rather than "Matulović lost."

What do the great players do in such situation?

Reshevsky just played on against Fischer, a queen down.
https://www.chessgames.com/perl/chessgame?gid=1008376 

Capablanca just played on against Sämisch, a piece down.
https://www.chessgames.com/perl/chessgame?gid=1066901 

its the modern age, everyone wants to win even if its dirty ;-;

@LordErenYeager wtf

People make blunders. At any time your opponent could drop a piece, especially lower rated players. At any time you could find a brilliant tactic that wins. Your opponent could be extremely weak in endgames.  You could create complications that make him  lose on time.  Of course if your opponent is rated hundreds of points higher than you, you're probably wasting your time. I recently played a game where I was a minor piece down, but my opponent only had about 3:40 left on his clock and I had something like 9:00.  I was creating complications, and he suddenly resigned. Perhaps he had sudden issues to deal with at home. I was disappointed, but I gladly took the rating points.

I think it depends - sometimes it's fun and educational to play out the end game even if you are losing. I sometimes ask the opponent to resign and rematch if the end game is boring to me. I'm currently winning against two players who haven't resigned and have chat disabled. I do find that a bit annoying.

I never consider my opponent who doesn't resign in lost positions as a play with bad manners or etiquette. I don't resign either. I have so many lost or drawn games that I were winning by 3+ points and vice versa I have saved and even won few games where I was losing by 3+ points. Level of play I'm currently on still allows huge comebacks or drops so why would I blame the other person for not resigning. I think this mindset I have will change once I reach master title if that ever happens or maybe even before but right now everyone up to 1800 should never resign and there is no single thing you can do about that to ever change my mind :) I'm not doing anyone any harm by playing on, they agreed to play ten minute game so I can't see how it is wasting time.

#2 if its so easy how come your rating isn't atleast 1200?

Are you okay with people playing 9 minutes of chess then?

I don't see the point in playing on just for the chance that my opponent will make an error. I do practice endings though, and I'm proud of my abilities there, even though they are modest. When I see when are close, but the opponent doesn't know how to end it, I keep going.