My problem is the apparent mutually exclusive options. When my male Lavellan says that he is going to stop Solas by any means possible, that doesn't preclude the option of persuading him there is another way to achieve his ends that doesn't result in wholesale destruction. It is that he finds it somewhat hard to come up with an argument that hasn't been used already and it is really frustrating when he asks why the world has to die and Solas' response is that he doesn't want to give him too much information, which sort of contradicts the idea that he wants to be shown another way because if that was the case then he really should give you all the available facts. He is angry at Solas for his deception but that is not the reason he is willing to kill him; he genuinely wants to save the world from destruction, not because he likes the way the current world is, politically, but nevertheless it is still his home and if you ignore the selfish nobility there are a lot of good people out there, not to mention the myriad of other creatures that would presumably die as a result of Solas' plan. If you choose the alternative option of saying that you support his aim of saving the elven people (but not his means I might add - though that is my own interpretation of the response) then he says there is no glory in it. I actually found that response somewhat insulting since my lad wasn't looking for glory; he genuinely wants a better life for all elves in Thedas and doesn't mind if he doesn't get the credit for bringing that about. So clearly taking that response is meant to indicate that you do support his plan and it is all about elven glory, which is why I reloaded and opted for the non-elven one. It is also why I'm annoyed that the elven specific response suggests you are in favour of his plan.
The reason I find the redeem option more appropriate to my female romanced Lavellan is because she has got that much closer to Solas; she also wants to save the world from him but she wants to save Solas too. She clearly has touched him in some deeper way because he still seems to be watching her. To be honest, though, whilst she'd give her own life to save Solas, she certainly wouldn't give the life of every other person/creature in the world, so ultimately if there are no other options open to her, she would kill him.
This is why I hated the whole idea of choosing either redeem or destroy because it makes your character's response too paragon/ruthless and I don't feel the situation is that simple.