In the chapter The Seven Potters in Deathly Hallows, we see that Lupin is aghast when he learns that Harry used Expelliarmus against Stan Shunpike (who was acting as Death Eater).
Despite going through the conversation that follows, I'm still unclear about what Lupin actually expected Harry to do?
Lupin looked aghast.
‘Harry, the time for Disarming is past! These people are trying to capture and kill you! At least Stun if you aren’t prepared to kill!’
Deathly Hallows - page 64 - Bloomsbury - chapter four, The Seven Potters
‘So you think I should have killed Stan Shunpike?’ said Harry angrily.
‘Of course not,’ said Lupin, ‘but the Death Eaters – frankly, most people! – would have expected you to attack back! Expelliarmus is a useful spell, Harry, but the Death Eaters seem to think it is your signature move, and I urge you not to let it become so!’
Deathly Hallows - page 64 - Bloomsbury - chapter four, The Seven Potters
The thing that is confusing for me is Lupin saying "of course not" to Harry's remark, since I could not think of any spells that could be used instead - since everything created the possibility of him falling off his broom. Is this just a general-life conflict that we can ignore (i.e. "I don't think you should kill him but do attack back, even if that kills him"?), or are there other possibilities?
Edit: This question is not a duplicate of this question since the latter focusses more on why Lupin (or any other Order member) did not foresee Expelliarmus being spotted as Harry's signature move. My question, on the other hand, is concerned with what they think would be a good solution (in an aerial battle like this, specifically) even if they did foresee the whole Expelliarmus fiasco.