How about sucking the souls out of the enemy to preserve the lives of your own soldiers and townsfolk? Only on paper can ethics be divided into black and white.
If your enemy raises a titanic army of demons and undead in order to protect his people. Can he be truly labeled as evil if he only did so because you have been trying to kill him and his people by conjuring "good" things and sieging him with unicorns and angels?
Are you mad
I am in the right. I've got the unicorns
on my side, for pete's sake!
Now that sounds weak actually, you are still sucking out the souls of some living creature and sending it into oblivion, not exactly a good thing, no matter the circumstances, and while undead could be argued depending on several circumstances, consorting with demons isn't exactly a terribly good thing and would probably come back to haunt your arse, on the other hands using angels and unicorns for evil wouldn't be good either, although on the other hand, would they do it if what they were doing was bad ? Probably not.
Before you go into good and evil, you have to define good and evil. And trying to define good and evil isn't just a lesson in futility, but it's also completely ridiculous. Good and Evil are, as always, points of view, based on differing points of interest (or a variety of moral & ethical rulesets).
Who's to say that sucking the soul out of someone and sending it into the flames of oblivion isn't the good thing to do, in a case such as that? I think the question, rather than a question of good or evil, would be one of "Does the ends justify the means?". There's nothing inherently good or evil in any action. Since we can't define it, it becomes a matter of opinion, where the judgement lies in the eye of the beholder.
Is it "evil" to shoot someone, for example? Some would adamantly argue "yes!", while others would shrug with a casual "of course not". Magic is a weapon, just like a gun, and for that I can only say; 1) "Guns don't kill people. People kill people." and 2) "Good. Bad. I'm the Guy with the gun.".
As it is, you don't really provide anything convincing to your arguments, just raise a bunch of situations that don't really prove anything.
You can't prove something that by it's very nature is not a fact.