Is not-resigning in completely losing positions considered disrespectful?

My friend told me not resigning in a losing position is a good idea to train the endgame converting skills, and some games might be saved. But I felt really guilty doing that. For example, in this winnable-even-for-me position, my opponent, with over a minute on the clock, managed to blunder the win. lichess.org/IfHpY5Gb/black#108 Is it unethical or disrespectful to play on in those situations?

It is not disrespectful to play to the bitter end and try to force an opponent's mistake. Your opponents may get frustrated because they have to play till the end but you should not feel guilty by doing that. The only reason that many higher level players do not play in losing positions, especially in long games, is because they know that their opponent will not make a simple blunder so there is no reason to play on. They also have good knowledge on endgames so they know when the game is completely lost.

its got nothing to do with respect. its your choice. if you refuse to resign and your opponent is so sure that hes going to win then he should play it out or resign if hes too bored.

There are many endgames that are technical wins, but may not be easy for your opponent to convert. Some are extremely challenging to convert. You are fully entitled to test your opponent's skills in doing so.

Personally, the heuristic I use to decide if I want to resign is basically: Is it interesting to me to keep playing this game? If it's a position that is technically challenging, I will play it out. If it's a boring position that is obviously lost (KQ vs K for example), then I will probably resign very quickly.

So the answer is that it's disrespectful *sometimes*. By playing on there is an implied declaration you are making: 'I think there is a decent chance you may blunder this'. That is a reasonable statement to make to a 1500 player in ANY game in ANY position, but if your opponent is 2200 and you're 1700 playing a completely lost position, that is a rude implied statement to make and you are certainly irritating them by wasting their time and playing on.

I'm a 2200 player and I prefer if my 1700 opponent plays on, I think fighting spirit will translate into elo eventually. And a touch of arrogance though not pleasant in conversation, is useful for improving at chess. That said letting 30 minutes tick down in a completely losing classical game to waste your opponents time is weak. If you want to play on, play on. But don't punish your opponent for outplaying you by going to watch youtube video's while your clock is running.

Yes, not resigning is acceptable as long as you didn't run down your clock. But sometimes resigning is just for avoiding humiliation like the famous 6 knights and 6 bishops games by "some player".
For example, that position shown is an easy win even for an 800 player. I would promote to two bishops. Do you want to get checkmated by 2 bishops?

Depends. If there is some life in the position you can try and make something happen. However that 2 pawns vs lone king game is not even a problem for a chimp. If its a bullet situation everything goes but what is the point of playing with a lone king vs a KQ?

It is considered respectful to fight to the very end.

How long you play on for is a function of your assessment of your opponent's quality of play. If he was playing very well you would resign earlier and likewise if he was playing poorly and making mistakes you would hang on for longer.
So, no one should complain when their opponent doesn't resign because it simply means they weren't playing well enough to make their opponent feel hopeless enough to resign at that point. Play better and you will see your opponent resign earlier, on average.